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.