-The other type of masquerading that mmailid turns on is envelope "From:"
-masquerading based on draft contents. When a user explicitly specifies a
-"From:" header in a message, \fInmh\fR uses it rather than constructing its own.
-However, the SMTP envelope "From:" and the "Sender:" header are set to the
-user's real address. Turning on mmailid prevents this latter behavior. This is
-useful when the user wants to pretend to be sending mail "directly" from a
-remote POP3 account, or when remote mail robots incorrectly use the envelope
-"From:" in preference to the body "From:" (or refuse to take action when the two
-don't match).
+"username_extension", when specified on the "masquerade:" line, allows a second
+type of username masquerading. If the user sets the \fB$USERNAME_EXTENSION\fR
+environment variable, its value will be appended to the actual login name. For
+instance, if I am dan@company.com, and I set \fB$USERNAME_EXTENSION\fR to
+"\-www", my mail will appear to come from "dan\-www@company.com". This is meant
+to interact with qmail's "user\-extension" feature, where mail sent to
+\fIuser\fR\-\fIstring\fR will be delivered to \fIuser\fR. Likewise, those using
+versions of sendmail for which "plussed user" processing is active can set
+\fB$USERNAME_EXTENSION\fR to "+\fIstring\fR". These MTA features are useful
+because they allow one to use different email addresses in different situations
+(to aid in automatic mail filtering or in determining where spammers got one's
+address) while only actually having a single account. Note that
+\fB$USERNAME_EXTENSION\fR is only appended to the username when \fIpost\fR is
+generating "[Resent\-]From:" lines and the SMTP envelope "From:". \fIinc\fR,
+for instance, will not try to read from a maildrop file called "dan\-www" (to
+recall the earlier example).
+
+"draft_from" controls the most powerful type of address masquerading. Normally,
+when a user explicitly specifies a "From:" header in a draft, \fInmh\fR uses it
+rather than constructing its own. However, to discourage email forgery, the
+SMTP envelope "From:" and a "Sender:" header are set to the user's real address.
+When "draft_from" is turned on, though, the envelope "From:" will use the
+address specified in the draft, and there will be no "Sender:" header. This is
+useful when a user wants to pretend to be sending mail "directly" from a remote
+POP3 account, or when remote mail robots incorrectly use the envelope "From:" in
+preference to the body "From:" (or refuse to take action when the two don't
+match). Note that the MTA may still reveal the user's real identity (e.g.
+sendmail's "X\-Authentication\-Warning:" header).