The Encrypted: header is used to describe a translation that has been performed on the body of the mail message. Although encryption is implied, other forms of translation, such as compression and uuencode(1), are perfectly legal.

The sendmail program ignores the Encrypted: header. This header is intended for use by MUAs. Unfortunately, most (if not all) Unix MUAs also ignore this header. The form for the Encrypted: header is:

Encrypted: prog key

The field contains one mandatory item, the prog, and one optional item, the key. The prog is the name of the program that was used to transform the message body. The optional key is a decryption key.

If translating the message body into a different form, be aware that many versions of sendmail strip the eighth bit from all bytes of the body during transmission.

The Encrypted: header is deprecated and was dropped from RFC2822. The Encrypted: header should never be declared in the configuration file.