$=e

contains the Content-Transfer-Encodings that can be 8?7 bit encoded. It is predefined to contain 7bit, 8bit and binary.

$=k

set to be the same as $k, that is, the UUCP node name.

$=m

set to the set of domains by which this host is known, initially just $m.

$=n

can be set to the set of MIME body types that can never be eight to seven bit encoded. It defaults to multipart/signed. Message types message/* and multipart/* are never encoded directly. Multipart messages are always handled recursively. The handling of message/* messages are controlled by class $=s.

$=q

A set of Content-Types that will never be encoded as base64 (if they have to be encoded, they will be encoded as quoted-printable). It can have primary types (e.g., text) or full types (such as text/plain). The class is initialized to have text/plain only.

$=s

contains the set of subtypes of message that can be treated recursively. By default it contains only rfc822. Other message/* types cannot be 8?7 bit encoded. If a message containing eight bit data is sent to a seven bit host, and that message cannot be encoded into seven bits, it will be stripped to 7 bits.

$=t

set to the set of trusted users by the T configuration line. If you want to read trusted users from a file, use Ft /file/name.