mailsnarf outputs e-mail messages sniffed from SMTP and POP
traffic in Berkeley mbox format, suitable for offline browsing with
your favorite mail reader (mail(1), pine(1), etc.).
OPTIONS
-i interface
Specify the interface to listen on.
-v
"Versus" mode. Invert the sense of matching, to select non-matching
messages.
pattern
Specify regular expression for message header/body matching.
expression
Specify a tcpdump(8) filter expression to select traffic to sniff.