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
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.