WO2005096573A2

WO2005096573A2 - Method and device for refusing unwanted e-mail

Info

Publication number: WO2005096573A2
Application number: PCT/EP2005/001623
Authority: WO
Inventors: Bruno Bozionek; Thomas Hanna; Klaus-Josef Kunte; Rainer Zimmermann
Original assignee: Siemens Aktiengesellschaft
Priority date: 2004-01-23
Filing date: 2005-02-17
Publication date: 2005-10-13
Also published as: DE102004012490B4; DE102004012490A1; WO2005096573A3

Abstract

The invention relates to a method for refusing unwanted electronic messages that are transmitted over network nodes of a communications network to a destination network node assigned to a recipient. A network node, which has received a message addressed to the recipient, forwards this message in an unmodified form to the destination network node only when the message is labeled with a message identification in which an indication of a message category is contained that is allocated beforehand by the recipient and stored in the communications network, and optionally additional classification features. The invention enables an improved adaptation of the refusal measures to the needs of the recipient.

Description

Method and device for preventing unwanted e-mail

description

Technical field

The invention relates to a method and a device for preventing unwanted messages, in particular e-mail.

State of the art

With the globally increasing number of participants on the Internet, the Internet is also increasingly used for advertising purposes. In direct email marketing, the intended direct influencing of the consumer takes place by sending mass emails. These bulk emails are often undesirable for recipients. For the advertiser, on the other hand, this form of marketing is inexpensive, since it is essentially exhausted in creating an advertising message, which - compared to the printing and postage costs incurred by print media or the telephone costs incurred by telephone marketing - is inexpensive and almost simultaneously to a very large group can be sent by addressees. In order not to have to reveal the sender's own identity, the sender usually uses a mailbox or a link to the product's website. For unwanted electronic mass messages, different terms are used in the literature depending on the transmission medium, e.g. for a mass email

"Unsolicited Bulk Email" (ÜBE), "Unsolicited Commercial Email" (UCE) or "Junk Email". The acronym SPAM, which is borrowed from advertising, appears more appropriate, which in the following is to be understood as meaning an unsolicited email sent to a large number of recipients, which conveys an advertising message and in which the identity of the sender is deliberately hidden or falsified from the recipient. Sending SPAM emails is becoming a rapidly growing problem. SPAM emails are more than a harmless nuisance. They cause significant 5 problems in the transmission of messages in the communication network. For example, a computer on the Internet may be overloaded by an attack data stream or fail entirely. On the recipient side, there are high costs for the inspection and elimination of the unwanted electronic mail.

A large number of methods are known for preventing unwanted electronic messages, all of which do not solve the problem satisfactorily.

15 A concept is known from the literature (Abadi, M .; et al: "Bankable Postage for Network Services", Eight Asian Cumputing Science Conference, 2003, Springer Verlag 2003, Published in the LNCS Series), in which a broadcaster is represented by a Interacting with a ticket server acquires a "ticket" with

20 which he marks his email and sends to one or more recipients using SMPT (Simple Mail Transfer Protocol). The recipient or his ISP (Internet Service Provider) confirms the receipt of this marked email to the ticket server, whereby the "ticket"

2.5, “will be rtev. The "ticket" is similar to an electronic ⁵ stamp, since a new "ticket" must be requested for each new email, which means a doubling of the SMTP traffic on the Internet.

30 Another option is to use so-called filters, which are computer programs that use lists, for example, to exclude certain senders or to allow them exclusively. For example, you can use a filter that works with a so-called black list

35 Extract messages from which the recipient does not want to receive emails. However, this method has the disadvantage that a SPAM sender can circumvent the black list simply by appearing with a new address. On However, the constant updating of a black list means that this black list is becoming more and more extensive. In order to keep a black list on a mail server up to date, considerable administrative effort is required. In contrast, a filter that works with a so-called white list only allows messages with a trustworthy email address. The disadvantage here is that messages that come from an unknown sender are not forwarded until the recipient adds the address of this sender to the white list. In order to give an unknown sender a chance to contact the recipient, these filters are often equipped with an accreditation function. This means that the filter causes an e-mail to be sent automatically to this sender when an e-mail with an unknown origin is received, asking him to make his identity known. If the sender complies with this request, the filter automatically adds its address to the white list. However, there are systems that - although they are not SPAM transmitters - cannot respond to this request. This

Addresses must be entered manually in the white list, which is correspondingly complex. A method which works with lists of desired and unwanted senders is known, for example, from US Pat. No. 6,023,723.

Another option is to analyze the header or the content of the email. When analyzing the header, it can be checked, for example, whether the information about the sender and recipient is in the prescribed format and whether it is conclusively specified, whether the Internet address and the domain name can be verified by an administrative center, and whether the transmission path to the individual mail servers is plausible. The analysis of the content of the email can also consist of searching for specific words or combinations of words in the transmitted text. Such a method is disclosed for example in US 6,161,130. The disadvantage here is that it is difficult to make a clear separation of the content between SPAM e-mails and wanted messages. On the one hand, this is due to the fact that the reception of a certain type of message is undesirable for one recipient, while another recipient wishes to receive this type of message. A fundamental problem of defense mechanisms implemented centrally on a mail server is that it is difficult to deal with individual definitions of connected recipients. A central countermeasure can, however, also be legally questionable, since a recipient may attribute meaning to a filtered out information.

From the international patent application W 02/082226 A2, a filtering method for e-mails is known which eliminates unwanted e-mails according to certain filter criteria. The decision on how to deal with an unwanted message rests with a so-called "delivery service", which is: represented by a POP server of the recipient. Unwanted emails are only intercepted at the recipient end and therefore put a strain on the communication network.

In the American patent application US 2002/0120600 AI, a rule-based sequence control for electronic messages is proposed, in which a decision is likewise made in a client-side server as to whether a message to be regarded as undesirable is rejected, displayed or modified. Since this decision is also made here in the receiver-side server, the network is burdened by the transport process of unwanted messages.

The American patent specification US 6,266,692 B1 requires a valid passcode for the transmission of an email. Only emails that contain a valid passcode are transported to the recipient. Emails that contain an incorrect passcode are automatically deleted from the server's mail server. However, if an email does not contain a passcode, it will it is transported to the recipient's pop server, which takes up corresponding resources in the network. In addition to these methods, the action of which starts on the recipient side, methods are also known which aim to ensure that many users in a network act jointly against the spread of SPAM. Messages in the shared network are analyzed and compared. For example, by forming a checksum z: u of each email received, a characteristic of the email can be generated, by means of which an electronic message can be clearly identified. As soon as a recipient receives a SPAM, he reports this to a central point in the network, which _^ filters out the unwanted message with its own characteristics.

All of these known methods have in common that they cannot respond individually to recipients whose assessment regarding undesired messages varies and can fluctuate and require a considerable administrative effort.

Presentation of the invention

The present rf-ind ^* unrg ^: i "is based on the task" to specify a method and a device for preventing unwanted electronic messages in such a way that it can be better matched to the needs of a recipient and integrated in a communication network without great administrative effort ,

This object is achieved by a method having the features of claim 1, and for a device having the features of claim 20. Subclaims refer to advantageous configurations.

According to a basic idea of the invention, a receiver stores information in the communication network, which of a sender can be called up from the communication network and which is added as a message identifier when creating an e-mail. In contrast to previously known countermeasures, which all require activity on the part of the recipient, the method according to the invention works indirectly: before sending an email, the message identifier must be acquired by the sender and the email must be identified. In a sense, the comparison to a stamp is obvious since the further transport of the e-mail in the communication network depends on this "electronic stamp". As will be shown in the following, the identification according to the invention goes beyond the function of a "ticket", since this "end-to-end" is exchanged between sender and receiver and is used several times. A special "ticket server" is not required. The information contains, on the one hand, an indication of a message category, ie the classification of those messages which the recipient would like to receive and possibly further typing features, which are explained in more detail below. This allows e-mails that do not correspond to this characteristic to be picked out during transmission in the communication network. On the other hand, the stored information also contains a regulation specified by the recipient, ^" which specifies how to deal with e-mails addressed to the recipient in the communication network. The identification according to the invention is analyzed in the communication network by a network node and evaluated in such a way that only marked messages are forwarded to the recipient's mailbox, which contain the information previously given by the recipient with the indication of the message category. The decisive advantage of the identification of the email according to the invention is that only a limited group of senders is permitted, who, until revoked, may store electronic messages in the recipient's mailbox. A SPAM e-mail that does not contain this message identifier will be intercepted early on the network However, the method according to the invention also means that advertising emails are transmitted intentionally if the recipient wishes to receive them. If he no longer wishes this at a given point in time, he changes the specification of the message category in the communication network. This means that the defense measure can be better tailored to the recipient's current needs. The implementation in an existing e-mail system is easily possible, since only the software for creating the e-mail (message user agent) and the corresponding software on an evaluating network node have to be designed in accordance with the function explained.

The method according to the invention has the following steps: a) sending a message addressed to the recipient through a communication terminal device of a transmitter, the message identifier including: an indication of a message category assigned by the recipient; an address of a requester to which the recipient's information stored in the network was transmitted on request; a sender-specified specification of a message category with which the sender identifies the message sent by him; an address assigned to the sender. b) Receiving the message by a network node, which evaluates the message identifier and only forwards unmarked messages unchanged to the destination network node, in which the requesting address matches the sending address and the recipient assigned the message category assigned by the sender.

A preferred embodiment of the method is characterized in that the message identifier consists of a sequence of instructions which is formed by software that can run on the evaluating network node, by which, in the event of a mismatch between the requesting and the sending address, the message is automatically identified as undesirable is before it is forwarded to the destination network node. Through this software there the recipient issues an automatically executable regulation on how to deal with an e-mail addressed to him in the communication network. Since this rule can be updated by the recipient at any time, the countermeasure can be adapted to the current needs of the recipient.

A further preferred embodiment of the method according to the invention is characterized in that the message identifier contains a sequence of instructions which form software that can run on the evaluating network node, by which, in the event of a mismatch between the requesting and the sending address, and / or in the event of a mismatch between the message category assigned by the recipient and the sender, the message is automatically deleted. Due to the automatic deletion process, the recipient's mail box is kept free of unwanted messages.

It is particularly advantageous if the transmission of the message identifier to the requesting address is made dependent on whether the requesting address can be found in a directory (DNS). This ensures that the message identifier is only output to those communication participants whose address can also be followed rüσkve.

In a first preferred variant of the invention, the message identifier is stored by the recipient on a target network node assigned to it. In this variant, the identification of the e-mail is preferably carried out by the following steps: 1) sending a request signal from the communication terminal device of the transmitter to the target network node; 2) transmitting the message identifier from the destination network node to the communication terminal of the transmitter; 3) insertion of the message identifier in the header of the electronic message by the communication terminal of the transmitter, so that the message identifier forms an inseparable part 5 of the email.

In a second preferred variant of the invention, the message identifier is stored by the receiver on an access network node assigned to the transmitter. It is advantageous here that the transmission of an undesired e-mail can be prevented at the beginning, when it is introduced into the communication network. In this variant, the identification of the e-mail is preferably carried out by the following steps: 15 1) sending a request signal from the communication terminal of the transmitter to the access network node; 2) transmitting the message identifier from the access network node to the communication terminal 20 of the transmitter; 3) inserting the message identifier into the header of the electronic message by the transmitter's communication terminals.

^'25 ^~ ~ ^"rn a dritten- evorzugten variant of -Erfindung-'wird the message identifier from the receiver at a Public Service or private stored and retrieved from a service. In this variant, the identification of e-mail 30 is preferably performed by the following steps : 1) sending a request signal from the communication terminal of the transmitter to the public or private server; 2) transmitting the message identifier from the public or private server to the communication terminal of the transmitter; 3) inserting the message identifier into the header of the electronic message by the communication terminal of the transmitter. It can be advantageous here if the transmission of the 5 message identifier is made dependent on a fee payment by the transmitter to the operator of the public or private server.

It is also advantageous if the recipient who recognizes when an email is retrieved 10 that the actual content of a sender's message does not match the message category assigned by the sender stores a message identifier by means of which messages from this sender are automatically deleted. The new 15 assignment of a news category effectively changes the reputation of this broadcaster; if necessary, an update of the message category stored in the network no longer sends any further messages from this sender into the recipient's mailbox. It can also be expedient for the message identifier to contain a parameter which limits the validity of the electronic message to a predetermined period of validity. As a result, a recipient ^~ 25 'can cause the e-mail to be deleted itself after the validity period has expired, or to be provided with a "SPAM" label and, if necessary, to be stored in a SPAM folder.

It can also be expedient for the message identifier to contain a parameter which limits the validity of the message identifier to a predetermined period of validity. This can cause a sender to request that a new message identifier be automatically requested after the validity period has expired. A packet-switching network, in particular the Internet, is preferred as the communication network, in which the transmission of the electronic message between the network nodes is established by the simple mail transfer protocol (SMTP), which is widespread on the Internet as the de facto standard.

The advantage is that the message identifier only has to be obtained once and can then be used several times to send emails.

It is advantageous if the email has a message header with a first field that contains the requesting address. This prevents the transmission of e-mails in which the requesting address and the sending address do not match.

In order to protect the message identifier from misuse, it must form an inseparable unit with the message header. This restricts manipulation of the message identifier and one

Differentiation to binary and code attachments such as Email worms and Trojans guaranteed.

Brief description of the drawing

The invention is explained below by way of example with reference to the accompanying figures. Show it:

Figure 1 is a schematic representation of the structure of an email compared to a letter;

Figure 2 is a schematic representation of a conventional communication network for the transmission of emails;

FIG. 3 shows a schematic sequence of the method according to the invention in a first exemplary embodiment; Figure 4 is a schematic representation of the method according to the invention in a second embodiment;

Figure 5 is a schematic representation of the inventive method in a third embodiment.

Figure 6 is a schematic representation of the structure of a message identifier.

Implementation of the invention

FIG. 1 shows the structure of an e-mail, as it is transmitted on the Internet by the SMTP protocol, in comparison to the letter post. Analogous to a conventional letter, an email 17 consists of an envelope E and the actual content of the message. The envelope contains all the necessary sender and recipient data, which are created in digital form using the SMTP protocol. In contrast to the content that is readable by the recipient, information in the envelope remains hidden from the user. The message content is divided into a message header 14 (header H) and a message body 15 (body B). An empty line 16 separates the message header part 14 from the message body part 15. The TsJachrichteriköpfteil 14 is in turn composed of different fields (field 1, ... field n). For example, the sender, recipient, date and subject can be found in the header of the email. However, this information in the header can be set as desired by the sender of the email. In particular, they do not have to match the information in the envelope. It may be that the content of a message in the header is directed to a first address, but the message is in an envelope with a second address appearing on it. According to the SMPT protocol, the email is then sent to the second address on the envelope. The SMPT protocol removes the entries freely selectable by the sender, only the delivery notes of the individual Network nodes that were involved in the transmission remain. Usually only the Internet address can be recognized by the sender. It is therefore difficult to find out the actual sender from the e-mail received.

In Figure 1, the message identifier according to the invention is represented by a field "NKZ", which is identified by reference numeral 13. As stated above, the message identifier 13 contains a sequence of instructions that can be executed on the platform of an evaluating computer.

FIG. 2 schematically shows the structure of a communication network 23 for transmitting an e-mail from a sender 19 to one or more receivers 21. The communication network 23 consists of a message handling system (MHS) and a message transport system (MTS ). In the outer part of the message handling system, the human-machine interface is manufactured by a so-called message user agent (MUA), which is usually front-end software that is based on a communication terminal device, for example a personal computer of a transmitter or Recipient, expires. They implement the functions for creating, managing, sending and receiving an email. Programs with the "

Product names Netscape® Messenger®, Microsoft® Outlook®, Microsoft® Exchange®, America OnLine® or Eudora® known. The actual transport of the electronic message is carried out by so-called message transfer agents (MTA), each of which is a network node computer with appropriate software, which handles the further transport of the message by the network to a destination network node 18 according to the store-and-forward principle , The destination network node 18 stores the e-mail in a mailbox of the recipient 21 until the recipient has sent the e-mail through it

Communication terminal devices 22, for example a PC, picks up using the POP protocol. FIG. 3 shows the sequence of the method according to the invention in a first exemplary embodiment in a simplified representation. In a first step, an e-mail sender A requests from an e-mail recipient C (the actual addressee to whom he has sent an e-mail) through his communication terminal 7, which is identified in the drawing in FIG. 3 by an arrow with the reference number 1 Would like to transmit) a recipient-side information about a message category and possibly further typing characteristics. This specifies the class of messages that the e-mail recipient C would like to receive. This information was previously stored by the receiver C on a target network node assigned to it. In a second step, which is identified by the arrow 2, this specification of a message class is transmitted from this target network node to the e-mail sender A. As with the request in step 1, the message identifier is generally transmitted via several network nodes of the communication network (message transfer agent (MTA) in FIG. 2). For the sake of simplicity, FIG. 3 shows only one e-mail server B, the special function of which will be explained in more detail below. The e-mail sender A now creates an e-mail addressed to the recipient C. He marks this with the received, recipient-side information, as well as ^" with a sender-side information of a message category. With the latter he characterizes the content of the message sent by him, eg advertising email. The message identification also contains the address to which The text of the e-mail is now created in a manner known per se by the editor function of the sender's communication terminal 7. When the e-mail is created, this e-mail is created in header 14 by the one shown above Message identifier 13. The identifier in the header 14 of the e-mail 17 has the advantage over an attachment that the information contained therein is better protected against misuse Manipulation is protected. In a third step (which is marked with an arrow with the reference symbol 3 in FIG. 3), this marked message 17 is sent and arrives at the above-mentioned e-mail server B. The e-mail server B checks the incoming and to C electronic message directed to the presence of a message identifier. When evaluating the message identifier, it is checked whether the message category assigned by the sender and the message category previously stored in the network by the receiver match. Furthermore, it is checked whether the sending address matches the address to which the recipient's specification of the message category was previously transmitted from the network. If this is the case in both cases, the e-mail is placed in the mailbox of recipient C (arrow with the reference number 4). If this is not the case, the message is processed in accordance with the program code contained in the message identifier, for example the message is forwarded changed to the recipient (arrow 4 in FIG. 3), the change may be that the email as Advertising email is flagged; however, the email can also be deleted automatically (arrow five in Figure 3).

In both cases, it can be provided that the result of the "^"" ^" evaluation of the message identifier is reported back from the evaluating server 9 to the server that specifies the message category. This feedback enables the e-mail recipient, an e -Mail sender received, trustworthiness registered and corrected if necessary. The registration can be carried out in such a way that the sender of the e-mail - depending on the frequency of the mismatch between the stated and actual content of the message - can be assigned different levels of trust the e-mail sender assigns the sender to a so-called white list or black list, and the trustworthiness of a sender can be corrected easily by using the Receiver updates the instruction it has stored in the network accordingly, ie stores changed information in the network.

The sequence of the method according to the invention is shown schematically in a second exemplary embodiment in FIG. The procedure differs from that in FIG. 3 in that the request when calling up the specification of the message category assigned by the recipient (step 1) is directed here to an access network node 10 (shown in simplified form in FIG. 4 as e-mail server B). The access network node 10 is assigned to the e-mail sender A. Here, too, this information is transmitted from the network to the requesting address in a second step (in the example shown in FIG. 4, this is the address of the e-mail sender A). In a third step, the one with the

E-mail sent with message identifier. This immediately reaches the evaluating network node, here the access network node 10. The access network node 10 proceeds exactly as already stated in the first exemplary embodiment. He checks the received e-mail for the presence of the message identifier and evaluates it as shown above, that is, the e-mail is either marked with a note in the ^" mailbox of the e-mail recipient if the characteristics specified therein do not match forwards (arrow 4), or deleted (arrow 5) Of course, in this exemplary embodiment as well, as explained above, feedback can be given to the e-mail recipient C, who decides whether he changes his or her information stored in the network or maintains.

The sequence of a third exemplary embodiment of the method according to the invention can be seen in a simplified illustration in FIG. In contrast to the examples shown in FIG. 3 and FIG. 4, in this variant of the invention, the message identifier is not acquired from someone on the The network nodes involved in the transmission of messages, but from a public service or private web service, represented as a public server 11. As the arrow with the reference symbol 1 indicates, a request signal is also sent to this public server 11 in a first step. In a second step, the message identifier is transmitted (arrow 2) from the public server 11 to the requesting address, here the e-mail address of the sender A. The latter again adds the message identifier to the e-mail. The marked e-mail is sent using the

Communication terminal device 7 of the e-mail sender A is introduced into the communication network and reaches an evaluating network node during transmission (e-mail server B in FIG. 5). The further course of the evaluation again corresponds to what has been said above, that is to say the electronic message is either discarded (arrow 5) or marked in the mailbox of recipient C (arrow 4). As the arrow 6 in FIG. 5 indicates, evaluating network nodes interact with the public server 11.

In an example, FIG. 6 shows components of a message identifier NKZ. The first part 24 is an indication of the message category (recipient message category) assigned by the recipient, ^" which the recipient of an e-mail has stored in the communication network, for example on a server or transmitted to a public service; this recipient-side indication 24 identifies that class of messages, wishes to receive the receiver. It is available from the communications _network., or from the Public service. the second part 25 consists of an assigned by the sender specifying a message category (sender message category), with which the sender characterizes the despatched by him content of the message The third part 26 is the address of a requesting party, that is to say the address to which the communication network or the public service has transmitted the message identifier (NKZ requesting party address) Message identification NKZ consists of the address of the sender (e-mail sender address). The fifth part 28 is the sequence of instructions issued by the recipient, which specify a regulation of how to deal with e-mails addressed to the recipient 21.

As can be seen from the schematic illustration in FIG. 6, the fifth part 28 contains information about further typing features: by specifying an NKZ

After a specified period of time has expired, appropriate instructions can trigger an action that, for example, leads to an automatic NKZ request. By specifying an e-mail validity period, an action can be triggered after a predeterminable time period, which, for example, leads to an automatic e-mail deletion. Further code segments 1 to n can contain information about code length, code type, code language version and code body. The message identifier can also contain a binary checksum via the NKZ.

Claims

claims

1. A method for warding off unwanted electronic messages (e-mails) which are transmitted via network nodes of a communication network to a destination network node assigned to a recipient, a network node which has received a message addressed to the recipient only then sending it to the destination - Forwards the network node unchanged if the message is identified by a message identifier, which contains a message category previously assigned by the recipient and stored by him in the communications network, comprising the following steps: a) A message is sent to the recipient by a communications terminal a sender, the message identifier containing: the recipient-specified specification of a message category; an address of a requester to which the recipient's information stored in the network was transmitted on request; an indication of a message category assigned by the sender, with which the sender identifies the message sent by him; 'an address assigned to the sender. b) Receiving the message by a network node, which evaluates the message identifier and only forwards unmarked messages unchanged to the destination network node, in which the requesting address matches the sending address and the recipient assigned the message category assigned by the sender.

2. The method according to claim 1, characterized in that the message identifier consists of a sequence of instructions that form executable software on the evaluating network node, by which, in In the event of a mismatch between the requesting and the sending address, the message is automatically marked as undesirable before it is forwarded to the destination network node.

3. The method according to claim 1 or 2, characterized in that the message identifier contains a sequence of instructions which forms executable software on the evaluating network node, through which, in the event of a mismatch between the requesting and the sending address, and / or in In the event of a mismatch between the message category assigned by the recipient and the sender, the message is automatically deleted.

4. The method according to any one of claims 2 to 3, characterized in that the transmission of the message identifier to the requesting address is made dependent on whether the requesting address can be found in a directory (DNS).

5. The method according to any one of claims 2 to 3, characterized in that in the case that the transmitting end specified message category is not ^'coincides with the actual -content-Na chricht, the stored message label is changed by the receiver.

6. The method according to any one of claims 1 to 5, characterized in that the recipient stores the message identifier on an assigned destination network node.

7. The method according to claim 6, characterized in that the labeling of the electronic message comprises the following steps: Sending a request signal from the communication terminal of the transmitter to the target network node; Transmitting the message identifier from the destination network node to the communication terminal of the transmitter; Insertion of the message identifier in the header of the electronic message by the communication terminal of the transmitter. 8. The method according to any one of claims 1 to 5, characterized in that the receiver stores the message identifier on an access network node assigned to the transmitter. 9. The method according to claim 8, characterized in that the labeling of the electronic message comprises the following steps: sending a request signal from the communication terminal of the transmitter to the access network node; Transmitting the message identifier from the access network node to the communication terminal of the transmitter; Insertion of the message identifier in the header of the electronic message by the transmitter's communication terminals.

10. The method according to any one of claims 1 to 5, characterized in that the recipient stores the message identifier on a public or private server that interacts with the evaluating network node.

11. The method according to claim 10, characterized in that the marking of the electronic message comprises the following steps: Sending a request signal from the communication terminal of the transmitter to the public or private server; Transmitting the message identifier from the public or private server to the communication terminal of the transmitter; Insertion of the message identifier in the header of the electronic message by the communication terminal of the transmitter.

10

12. The method according to any one of the preceding claims, characterized in that the recipient, if he recognizes that the actual content of a message of a transmitter does not match the message category assigned on the transmitter side, stores a message identifier by means of which messages of this transmitter are deleted.

13. The method as claimed in one of the preceding claims, characterized in that the message identifier contains a parameter which specifies the validity of the electronic message and / or the message identifier

25. Limits of validity.

14. The method according to any one of the preceding claims, characterized in that the communication network is a packet-switching network, in particular the Internet.

15. The method according to any one of the preceding claims, characterized in that the transmission of the electronic message between the network nodes is established by the simple mail transfer protocol (SMTP).

16. The method according to any one of the preceding claims, characterized in that the transmission of the electronic message between the sender and communication network or is established between the receiver and the communication network using the PostOf ice protocol (POP).

17. The method according to any one of the preceding claims, characterized in that 5 depositing and obtaining the message identifier by a secure protocol, selected from the protocol families (SIP / SMTP / HTTP). 18. The method as claimed in one of the preceding claims, characterized in that the electronic message has a message header with a field which contains the requesting address. 19. The method according to claim 18, characterized in that the electronic message has a message body part, that the message header part contains a reference to an attachment in the message body part, wherein the addition contains a sequence of instructions that can be executed on the platform of a network node.

20. Device for defense against electronic messages, -5 ^' a communication terminal device (7) "for producing an" e-mail (17) with a message identifier (13) which contains the following parts: a) a recipient-side specification of the message category (24), which a recipient (21) has stored in the communication network 0 (23) and which has been transmitted from the communication network (23) to the address of the requesting party (26) at the request of a requesting party; b) a sender-side specification of the message category (25) with which a sender (19) specifies the content of the e-mail sent by him5; c) the address of the requester (26); d) the address of the sender (27); a communication network (23) with a network node (MTA) for transmitting the e-mail from the sender to a recipient, an evaluating network node evaluating the message identifier and forwarding an e-mail to a recipient's mailbox unchanged only if the requesting address with the sending address and the information given by the receiver matches the information given by the sender of the message category.

10. The device as claimed in claim 20, characterized in that software (28) which can run on the evaluating network node is contained in the message identifier.

22 22. The apparatus of claim 21, characterized in that the software is designed such that in the event of a mismatch between the requesting and the sending address, the message automatically as

20 undesirable is marked before it is forwarded to the destination network node.

23. The device according to claim 21, characterized in that the software is designed such that in the case of

2.5 Mismatch between the requesting and the sending address, and / or in the event of a mismatch between the message category assigned by the recipient and the sender, the message is automatically deleted.

24. The device as claimed in claim 23, characterized in that the message is deleted after a period of time which is contained in a part (28) of the message identifier (13).

35