Email#Message header

An Internet e- mail consists of the header portion (of English for: " header " ) and the body ( the actual content of the message). The header contains a compulsory indication only one sender details and the date of creation of e-mail. In addition, the header of an e-mail containing a number of optional information. As a rule, find information about the path that the email has taken on the content of the message and the format and information to the recipients.

The header contains no necessary for the technical delivery of an e -mail information. Senders and recipients can be specified by the envelope sender and envelope To.

The structure of an e -mail is defined in RFC 5322 - here is no longer spoken of header in contrast to previous standards, but header field for the contents of a single header and header section for the entire head area of the e- mail (all headers together) used to avoid confusion.

Rendering and display

Many recipients are not interested or only rarely for all header lines. Therefore, most mail clients display by default only a small part of actually contained in the e- mail header lines. These are in particular the lines with the Tags:

More or all header lines are usually displayed only with the choice of specific options. These are very different depending on the mail client. Some mail clients (eg mutt ) can be configured, which header lines are displayed by default. Some e -mail clients to replace the header tags in the display by a national language equivalent.

Example mail

In the following example, e- mail, the header information that is displayed by most e -mail programs, shown in blue. The mostly hidden header information are orange, the body is gray. The first line contains the so-called envelope sender, which was communicated to the mail server when receiving the message - it is not part of the header, but it is preceded in mbox format and is otherwise often presented together with the header rows; it is not transmitted in the Simple Mail Transfer Protocol (SMTP) as part of the mail header, but with a special command. Here also, the actual recipient (Envelope To) is transmitted. The two through this SMTP command transmitted e- mail addresses add some additional mail server like real fields in the header (for example, as X - Envelope -From and X - Envelope-To ).

Received: by server1 ( Postfix, from userid 1000) id D344F45681; Mon, 4 Dec 2006 14:51:39 0100 ( CET )

Possible entries in the header

Entries in the e -mail header are separated by a line break (CRLF ). The e -mail header is separated by a blank line (CRLF CRLF) from the e- mail body.

Return-Path: "If undeliverable return to "

The optional located in the first line of the header. It specifies the address to which error notification should be sent back by the mail server. The mail server should grudge this value independently with the indication from the SMTP envelope.

Date: date of mailing and time

Mandatory RFC 5322nd The timing of sending the e-mail.

From: Sender

Mandatory RFC 5322nd One or more comma-separated email addresses that denote the or the sender of an e -mail. Most e -mail clients support only a single sender.

Channel: Technical sender

Is referred to the technical sender is other than in the From - header, it can be noted in the channel header. The Channel field must contain only a single e- mail address. Example: The e- mail address of a secretary sent an e- mail to the dictates of the bosses, belongs in the Channel field. The e- mail address of the Chief belongs in the From field. If the author of an e -mail and the technical senders are identical, the Channel field should not be used, otherwise both ( From and Sender field ) should be used.

Reply-to: Reply-to address

One or more comma-separated e- mail addresses, to which a reply to the e- mail should be sent (if different from the From field ).

To: The recipient

One or more comma-separated e- mail addresses to which the e -mail is sent primarily. Each addressee is also communicated to all other e- mail addresses.

CC: Carbon Copy, the copy

One or more comma-separated email addresses to which a copy of the e -mail is sent.

The term comes from the breakdown previously used. In this created when writing with a pen or typewriter hard copies by several sheets of paper, each with a carbon paper (english Carbon, coal ') were superimposed between.

When writing an email, this field is used to send copies to one or more recipients. With an entry in this field is symbolized at the same time that this email is not used directly to that user, but only " to observe " or " for information " has been sent to him. The entries in the CC field are displayed ( as opposed to the BCC field ) to all beneficiaries and are thus known.

Colloquially also from time to time (especially in the U.S.) incorrectly used " Courtesy Copy" as important for CC, which means " courtesy copy " means (English courtesy, politeness ' and copy, copy ').

BCC: Blind Carbon Copy BCC

The recipients of e-mails to one or more comma-separated email addresses that the so-called BCC field (of English: Blind Carbon Copy, dt mutatis mutandis BCC ) were listed, receive a copy of each sent e- mail without their address for the other specified recipient is visible. By addressing the BCC the privacy of the recipients of round -mails can be maintained and they are such as spambots protected, for example, before the address collection of malicious services.

Because users (including the BCC addressees ) are communicated to the mail server before transmission by e -mail, the principle can be technically easy to implement: BCC recipients are named as recipients in the subsequently transmitted e- mail then removes the BCC line or is transferred changed. However, the handling of the BCC line is not clearly defined. Depending on the implementation in the e -mail program and the mail server used involved the following possibilities:

• The BCC line is completely removed from the header of the e -mail prior to transmission. The message is, however, still delivered to all recipients. The BCC recipients do not see as the e -mail that they were out in the BCC field. If the BCC line from being an accidental identification when you click Reply to all only to the TO and CC recipients, but not the other BCC recipients is possible.
• The recipients listed in the To and CC line as obtained above a copy of the email from the BCC line was removed. The recipients listed in the BCC line, however, receive a copy, in the BCC line remains the same. Depending on the email program either each BCC recipient receives a copy, in only his e- mail address is available, or all recipients receive the same BCC line. In the latter case, it is a blind copy recipients possible to see all the other BCC recipients.
• The content of the BCC line is removed in the transfer. Persons who receive the e-mail via BCC can not identify mutually exclusive. All recipients but signaled that the e -mail was also sent as a blind copy.

Even if e- mail programs and servers typically proceed according to the first variant, one should be in doubt, do not leave it.

Subject: The subject

The subject ( in German also subject) establishes a relationship of the transmitter and / or receiver to a thing required action or an event. It is for the receiver an important brief information about the contents of the mail and should therefore not be missing. In view of the increasing number of unsolicited e -mails ( UBE / UCE / Spam ) grows the importance of the subject field, for often unwanted messages can be detected already at the subject.

More header lines

More information is automatically inserted into the header, both the mail client ( Mail User Agent ) of the sender and of the mail servers involved in the management of the mail ( mail transfer agents ). Taking the example of the rule to the Received lines the order and address of all mail servers involved in the shipping read. Further, where appropriate, information regarding a virus was exam or spam classification or filtering in the header lines of the e -mail.

Authenticity of the header information

Like all parts of an email message are not monitored and header lines on accuracy of content. The information displayed here are forgeable. So putting resourceful spammers usually fake header lines in order to disguise the real origin of the e -mail or spam filters to lead astray, so that their mail is delivered unfiltered. This includes header rows on a legitimate default mail program (and thus a human sender) to indicate or header lines, which feign an already-effective spam check, in the hope that the mail will then be forwarded by the spam filter unaudited.

Solely To Envelope can not be manipulated from the outside and are always on which e- mail address of the sender is actually used to send the e- mail to the respective mailbox. If this address is entered from the mail server in the header and supported by the E -mail provider Wildcard -mail addresses (eg username [email protected] in Gmail), users can each time you log on the internet to use your own email address and the sender of the of uniquely identify it used destination address (if it does not know that, as in the hydrolysis with Gmail example, all e- mail addresses of a particular pattern belong to an account, and another address is used ).