Programming Internet Email

Mandatory Headers

Each RFC 822 message has a number of headers that are mandatory. That is, they must be included in order for the message to pass through the mail system. Note that this does not infer that the message is guaranteed to reach its intended recipient, just that it possesses sufficient information to enter the mail system and transit it to a destination.

The mandatory headers are:

• Date

• From

• and either To or BCC

The Date header gives the time and date that the message was sent. It is generally generated by the first MTA that receives the message.

The From header provides the sender’s name. It should contain the email address of the person who caused the message to be sent. This header should never contain a list of addresses.

If the From header alone does not distinguish the actual sender, then the Sender header should also be present. This might occur if the person (or program) that sent the message is not the same person as the author of the message. The real author is represented in the From header, and the person or program that actually sent the message is represented in the Sender header.^[5]

Obviously, it is a good idea to tell the mail system where the message is going. Any MTA that speaks SMTP according to the standard will demand this information before accepting a message for delivery. It is still possible to give an MTA a bogus address that cannot be delivered, though. In this case, the message will end up in a dead letter box for an administrator to deal with. If ...