.bp 
.au "TSC \- intro.xx"

.c
The expn Program

.2
\f(BIexpn\fB uses sockets to directly connect to a remote
\s-1SMTP\s0 port to figure out how a mail aliases expands.

.2
This is just a simple version of the program.  Others have
written fancier version.

.2
It looks at its own 
.T $0
to know whether to use the \s-1VRFY\s0 or \s-1EXPN\s0.

.2
Even if you haven't run \f(BIh2ph\fB, it tries to 
guess network values.  It guesses wrong for Solaris.