Table 240: RFC 822 Electronic Mail Header Field Groups and Fields
Field
Group
|
Field
Name
|
Appearance
|
Number
of Occurrences Per Message
|
Description
|
Origination
Date
|
Date:
|
Mandatory
|
1
|
Indicates the date and time that
the message was made available for delivery by the mail transport system.
This is commonly the date/time that the user tells his or her e-mail
client to send the message.
|
Originator
Fields
|
From:
|
Mandatory
|
1
|
The e-mail
address of the user sending the message. This should be the person who
was the source of the message itself.
|
Sender:
|
Optional
|
1
|
The e-mail address of the person
who is sending the electronic mail, if different from the message originator.
For example, if person B is sending an e-mail containing a message
from person A on A's behalf, person A's address
goes in the From: header and person B's in the Sender:
header. If the originator and the sender are the same (which is commonly
the case), this field is not present.
|
Reply-To:
|
Optional
|
1
|
Used to tell
the recipient of this message the address the originator would like
the recipient to use for replies. If absent, replies are normally sent
back to the From: address.
|
Destination
Address Field
|
To:
|
Normally present
|
1
|
A list of primary recipients
of the message.
|
Cc:
|
Optional
|
1
|
A list of recipients
to receive a copy of the message (cc stands
for carbon copy, as used in old typewriters). There is no
technical difference between how a message is sent to someone listed
in the Cc: header and someone in the To: header. The difference
is only semantic, in how the recipient interprets the message. Someone
in the To: list is usually the person who is the direct object
of the message, while someone in the Cc: list is being copied
on the message for informational purposes.
|
Bcc:
|
Optional
|
1
|
Contains a list of recipients
to receive a blind carbon copy. These people receive a copy
of the message without other recipients knowing they have received it.
For example, if X is specified in the To: line, Y
is in the Cc: line, and Z is in the Bcc: line,
all three would get a copy of the message, but X and Y
would not know Z had received a copy. This is done either by
removing the Bcc: line before message delivery or altering its
contents.
|
Identification
Fields
|
Message-ID:
|
Should
be present
|
1
|
Provides a
unique code for identifying a message; normally generated when a message
is sent.
|
In-Reply-To:
|
Optional, normally
present for replies
|
1
|
When a message is sent in reply
to another, the Message-ID: field of the original message is
specified in this field, to tell the recipient of the reply what original
message the reply pertains to.
|
References:
|
Optional
|
1
|
Identifies
other documents related to this message, such as other e-mail messages.
|
Informational
Fields
|
Subject:
|
Normally present
|
1
|
Describes the subject or topic
of the message.
|
Comments:
|
Optional
|
Unlimited
|
Contains summarized
comments about the message.
|
Keywords:
|
Optional
|
Unlimited
|
Contains a list of comma-separated
keywords that may be of use to the recipient. This may be used optionally
when searching for messages on a particular subject matter.
|
Resent
Fields
|
Resent-Date:
Resent-From:
Resent-Sender:
Resent-To:
Resent-Cc:
Resent-Bcc:
Resent-Message-ID:
|
Each
time a message is resent, a resent block is required
|
For
each resent block, Resent-Date: and Resent-Sender: are required; the
others are optional
|
These are special
fields used only when a message is re-sent by the original recipient
to someone else, a process called forwarding. For example, person
X may send a message to Y, who forwards it to Z.
In that case, the original Date:, From: and other headers
are as they were when X sent the message. The Resent-Date:,
Resent-From: and other resent headers are used to
indicate the date, originator, recipient and other characteristics of
the re-sent message.
|
Trace Fields
|
Received:
Return-Path:
|
Inserted by
e-mail system
|
Unlimited
|
These fields are inserted by
computers as they process a message and transport it from the originator
to the recipient. They can be used to trace the path a message took
through the electronic mail system.
|