I was debugging a program that talks to sendmail, and couldn't figured out the best tcpdump options to use. Here what I used: tcpdump -i eth0 -X tcp port 25 However, some request/response were not shown completely. -- .~. http://toylet.homeip.net / v \ Linux 2.4.22-xfs /( _ )\ 10:28am up 15:34 1 user ^ ^ 1.02 1.00