980604-4 In e-mail, the name of the sender and the recipient are often specified both in the SMTP "envelope" and in the RFC822-heading. What is the difference in how this information is meant to be used by e-mail software.

Correct reply

The envelope information is used to control the transmission of messages to their recipients, and the transmission of delivery status reports, if requested, in the opposite direction.

The header information is provided for the user, and is usually only interpreted by the user or the client software used by the user. This information is often used to create recipient sets for replies. The header usually gives full information of all recipients for a message (except bcc recipients), while the envelope recipient list at delivery usually only shows the recipient, to which the message is delivered, and no other recipients.

It is important not to use the header information to control delivery, since this can cause wrong delivery (multiple copies, missed recipients, etc.). Some non-standards-compliant mailers, however, used to deliver on header receipients, but this incorrect behaviour is today very rare.

List of exam questions