+If nmh has been compiled with APOP #defined, the `\-apop' switch will cause
+\fIinc\fR to use APOP rather than standard POP3 authentication. Under APOP, a
+unique string (generally of the format
+<\fIpid\fR.\fItimestamp\fR@\fIhostname\fR>) is announced by the POP server.
+Rather than `USER \fIuser\fR', `PASS \fIpassword\fR', inc sends `APOP \fIuser\fR
+\fIdigest\fR', where digest is the MD5 hash of the unique string followed by a
+`secret' shared by client and server, essentially equivalent to the user's
+password (though an APOP-enabled POP3 server can have separate APOP and plain
+POP3 passwords for a single user). `\-noapop' disables APOP in cases where it'd
+otherwise be used.
+