+.PP
+Under normal circumstances,
+.B post
+uses the \*(lqFrom:\*(rq line in the message draft as the identity of
+the the originating mailbox. A \*(lqFrom:\*(rq line is required in
+all message draft. By default the message composition utilities such
+as
+.BR comp ,
+.B repl
+and
+.B mhmail
+will automatically place a \*(lqFrom:\*(rq line in the message draft.
+There are two ways to override this behavior, however.
+Note that they apply equally to \*(lqResent\-From:\*(rq lines in messages sent
+with
+.BR dist .
+.PP
+The first way is to supply a \*(lqSender:\*(rq line. The value of this
+field will be used as the originating mailbox identity when submitting the
+message to the mail transport system. If multiple addresses are
+given in the \*(lqFrom:\*(rq line, a \*(lqSender:\*(rq line is
+.BR required .
+If an \*(lqEnvelope-From:\*(rq line is supplied when multiple addresses
+are given in the \*(lqFrom:\*(rq line, a \*(lqSender:\*(rq header will
+be generated using the value of the \*(lqEnvelope-From:\*(rq line,
+.B if
+the \*(lqEnvelope-From:\*(rq line is not blank.
+.PP
+The second way is to supply a \*(lqEnvelope-From:\*(rq line. The value
+of this field will be used as the originating mailbox identity when
+submitting the message to the mail transport system. This will override
+both the value of the \*(lqFrom:\*(rq line and a \*(lqSender:\*(rq line
+(if one is supplied). The \*(lqEnvelope-From:\*(rq line is allowed to
+have a blank value; if the value is blank, then the mail transport system
+will be instructed to not send any bounces in response to the message.
+Not all mail transport systems support this feature.
+.PP
+The mail transport system default is provided in
+.I %etcdir%/mts.conf
+but can be overriiden here with the
+.B \-mts
+switch.
+.PP
+If nmh is using the SMTP MTA, the
+.B \-server
+and the
+.B \-port
+switches can be used to override the default mail server (defined by the
+.RI servers
+entry in
+.I %etcdir%/mts.conf
+).
+.PP
+If
+.B nmh
+has been compiled with SASL support, the
+.B \-sasl
+and
+.B \-nosasl
+switches will enable and disable
+the use of SASL authentication with the SMTP MTA. Depending on the
+SASL mechanism used, this may require an additional password prompt from the
+user (but the
+.RI \*(lq \&.netrc \*(rq
+file can be used to store this password).
+.B \-saslmech
+switch can be used to select a particular SASL mechanism,
+and the the
+.B \-user
+switch can be used to select a authorization userid
+to provide to SASL other than the default.
+.PP
+If SASL authentication is successful,
+.BR nmh
+will attempt to negotiate a security layer for session encryption.
+Encrypted data is labelled with `(sasl-encrypted)' and `(sasl-decrypted)' when
+viewing the SMTP transaction with the
+.B \-snoop
+switch. The
+.B \-saslmaxssf
+switch can be used to select the maximum value of the Security Strength Factor.
+This is an integer value and the exact meaning of this value depends on the
+underlying SASL mechanism. A value of 0 disables encryption.
+.PP
+If
+.B nmh
+has been compiled with TLS support, the
+.B \-tls
+and
+.B \-notls
+switches will require and disable the negotiation of TLS support when
+connecting to the
+SMTP MTA. Encrypted data is labelled with `(tls-encrypted)' and
+`(tls-decrypted)' when viewing the SMTP transction with the
+.B \-snoop
+switch.