Not really good with sendmail, the problem is works fine on all accounts but one? How should I investigate the proglem?

Seems likely your problem is not sendmail, but the config for that 1 user. More details?

OK when I try to use let's say formmail.pl it just hangs if I try form mail on any of my other accounts it works fine. I have tried to setup a couple perl scripts that use the /usr/sbin/sendmail path and just hangs. This is what I get from the one program:

Starting mailer UNIX
mailprog /usr/sbin/sendmail
open /usr/sbin/sendmail No such file or directory

But same setting in any other account and no problems. Any ideas?