Header (email)
An e-mail consists of the header section (from English for: "headline") and the body (English for " body ", the actual content of the message). The header only contains information about the sender and the date on which the e-mail was created. In addition, the header of an email can contain a number of optional information. There is usually information about the route taken by the email, the content of the message and its format, as well as information about the recipients.
The header does not contain any information necessary for the technical delivery of an e-mail, as this is transmitted within the framework of the transmission protocol. The sender and recipient are indicated by the envelope Sender and Envelope To . In most cases, however, this information is also available in the header, in particular the original recipient information (Envelope-To) and the transmission path (Received).
The structure of an e-mail is specified in RFC 5322 - in contrast to previous standards, the term header is no longer used , but the header field for the content of a single header and the header section for the entire header of the e-mail (all headers together) used to avoid confusion.
Presentation and display
Many recipients are not or rarely interested in all header lines. This is why most mail clients usually only display a small part of the header lines actually contained in the email. These are especially the lines with the tags :
- From
- sender
- To
- receiver
- Cc
- further recipients (visible)
- Bcc
- further recipients (are NOT displayed)
- Subject
- Subject
- Date
- Time of creation
Further or all header lines are usually only displayed with the selection of special options. These are very different depending on the mail client. With some mail clients (e.g. mutt ) you can configure which header lines are displayed. Some email clients replace the header tags with a local language equivalent when they are displayed.
Address details usually consist of a display name and the actual mail address enclosed in angle brackets (see the following example mail). For most address fields, a list of several address details is also allowed. Sometimes, depending on their configuration, email clients only display the display names.
Sample mail
In the example email below, the header information displayed by most email programs is displayed in blue. The mostly hidden header information is orange, the body is gray. The first line contains the so-called envelope sender , which was communicated to the mail server when the message was received - it is not part of the header, but precedes it in mbox format and is otherwise often displayed together with the header lines; in the Simple Mail Transfer Protocol (SMTP) it is not transferred as part of the mail header, but with a special command. The actual recipient (envelope To) is also transmitted. Some mail servers also add the two e-mail addresses transmitted via this SMTP command like real fields in the header (e.g. as X-Envelope-From and X-Envelope-To).
| From alex@mailgate.exam.ple Mon Dec 4 17:02:25 2006 | Envelope sender |
| Received: (qmail 12345 invoked by alias); Mon, 04 Dec 2006 13:51:40 +0000 Received: by server1 (Postfix, from userid 1000) |
Several "Received" lines show the path that the e-mail took from the sender to the recipient. Each server that forwards the mail adds its ID and date to the beginning of the mail. |
| Date: Mon, 4 Dec 2006 15:51:37 +0100 | Date of dispatch |
| Subject: The meaning of life | Subject of the email |
| Message-ID: <434571BC.8070702@example.net> | Unique string that identifies this email |
| From: Alex Sender <alex@example.net> | sender |
| To: Erwin Empfaenger <erwin@example.com> | receiver |
| Cc: ErwinsSekretariat <sekretariat@example.com> | Recipient of a copy of the email |
| Content-Type: text / plain; charset = UTF-8 | Type and character set of the body text |
| In-Reply-To: <134535224@example.com> | This e-mail is a reply to the e-mail with this message ID |
| The first blank line separates the headers from the message text | |
| Hello Erwin, we have to make an appointment. See you then, Alex |
Content ("message body") |
Possible entries in the header
Entries in the email header are separated from one another by a line break ( CRLF ). The e-mail header is separated from the e-mail body by a blank line (CRLF CRLF).
Return-Path: "If undeliverable back to"
The optional information is in the first line of the header. It specifies the address to which an error notification should be sent back from the mail server. The mail server should add this value independently with the information from the SMTP envelope .
Date: Date and time of sending
Mandatory according to RFC 5322 . The time the email was sent. In the simplest case, this entry - like other time information in the header - consists of values separated by spaces for the day (numeric), the month name (English text abbreviation), the year (four digits), the time (in the format "hh: mm") as well as their deviation from coordinated universal time (UTC). Optionally, you can specify a day name at the beginning of the entry (English text abbreviation and comma) and the seconds in time values ("hh: mm: ss"), as shown in the example above.
From: Sender
Mandatory according to RFC 5322 . One or more e-mail addresses separated by commas that identify the sender (s) of an e-mail. Most email clients only support a single sender.
Sender: Technical sender
The sender field contains a single sender address and thus indicates the mailbox responsible for the actual transmission of the e-mail. If the From field contains several addresses, the Sender field must be specified. Otherwise it is optional and can be used to specify a technical sender who differs from the originator of the mail. Example: The e-mail address of a secretary who sends an e-mail after the boss has dictated it could be entered in the sender field, the boss's e-mail address in the From field. Some issue tracking systems or mailing list programs use the sender field to identify the technical sender. If the author of an e-mail and the technical sender are identical, the sender field should not be used.
Reply-To: Reply address
One or more e-mail addresses, separated by commas, to which a reply to the e-mail should be sent (if different from the From field).
To: The recipient
One or more e-mail addresses, separated by commas, to which the e-mail is primarily sent. All other email addresses are also communicated to each addressee.
CC: Carbon Copy, the copy
One or more e-mail addresses, separated by commas, to which a copy of the e-mail will be sent.
The term comes from the previously used carbon copy. When writing with a hard pen or a typewriter, copies were made by superimposing several pages of paper, each with a carbon paper ( English carbon for "coal") in between.
When writing an email, this field is used to send copies to one or more recipients. An entry in this field symbolizes at the same time that this e-mail is not addressed to this user directly, but was only sent to him "for attention" or " for information ". The entries in the CC field (in contrast to the BCC field) are displayed for all recipients and are therefore known.
Is also from (mainly in the USA) incorrectly Colloquially Courtesy Copy used as important for CC, which as much as "courtesy copy" means ( English courtesy (dt .: "courtesy") and copy (dt .: "copy") ).
BCC: Blind Carbon Copy
The recipients of e-mails to one or more e-mail addresses separated by commas and listed in the so-called BCC field (from English: B lind C arbon C opy , dt. Analogously blind copy ), receive a copy of the sent E -Mail without their address being visible to the other specified recipients. By addressing in the BCC field, the privacy of the recipients of circular e-mails can be preserved. B. be protected from address collection by malicious services such as spambots .
Since the addressees (including the BCC addressees) are communicated to the mail server before the e-mail is transmitted, the principle can be implemented in a technically simple manner: BCC addressees are named as recipients; the BCC is then omitted in the e-mail that is subsequently sent Line or is transmitted changed. However, the handling of the BCC line is not clearly specified. Depending on the implementation in the e-mail program used and the mail servers involved , the following options arise:
- The BCC line is completely removed from the header of the email before transmission. However, the message is still delivered to all recipients. When the e-mail is received, the BCC recipients do not see that they have been entered in the BCC field. Due to the removed BCC line, (accidental) identification using the “Reply to all” program function is only possible for the TO and CC receivers, but not for the other BCC receivers. In such a case it makes sense to refer explicitly to BCC recipients.
- As above, the recipients named in the TO and CC lines receive a copy of the email from which the BCC line was removed. The addressees listed in the BCC line, however, receive a copy in which the BCC line is retained. Depending on the e-mail program, each BCC addressee will either receive a copy containing only their e-mail address, or all recipients will receive the same BCC line. In the latter case, it is possible for recipients of a blind copy to see all other BCC addressees.
- The content of the BCC line is removed during the transfer. People who receive the email via BCC cannot identify each other. However, the empty BCC field indicates to all recipients that the e-mail was also sent as a blind copy.
Even if e-mail programs and servers usually proceed according to the first variant, you should not rely on it in case of doubt.
Subject: The subject
The subject (in German also subject ) shows a relation of the transmitter and / or receiver to one thing, action required or event here. It is important brief information about the content of the mail for the recipient and should therefore not be missing. In view of the increasing number of unsolicited e-mails ( UBE / UCE / Spam ), the importance of the subject field is growing, as undesirable messages can often be identified by the subject.
More header lines
Additional information is automatically added to the header, both by the sender's mail program ( Mail User Agent ) and by the mail servers involved in managing the mail ( Mail Transfer Agents ). As a rule, the order and address of all mail servers involved in sending can be read from the Received lines. Information about a virus check or spam classification or filtering may also appear in the header lines of the email.
Authenticity of header information
Like all parts of an e-mail message, header lines are not checked for correctness and therefore do not provide any reliable information. Only "Envelope To" is authentic and always indicates which recipient address the sender actually used. The other header entries can be forged. Resourceful spam senders usually use bogus header lines to disguise the real origin of the email or to mislead spam filters so that their emails are delivered unfiltered. This also includes header lines that are supposed to indicate a legitimate standard mail program (and thus a human sender), or header lines that simulate a spam check that has already been carried out in the hope that the mail will then be passed by the spam filter forwarded unchecked. The most important aspect here is, however, that the sender cannot be determined, since even an existing sender address can be based on forgery.
Web links
- Header FAQ
- RFC 5322 Internet Message Format
- RFC 2076 Common Internet Message Headers
Individual evidence
- ↑ Blind Carbon Copy (Bcc) - this is how you send blind copies of your emails . ionos.de. February 28, 2019. Retrieved April 8, 2019.