I have a small LAN with a windows 2000 box, a slackware 9.1 box and redhat 9 mailserver/gateway.
The mail server is running sendmail and everything is working fine, i can send mail from the server (from mutt) or the windows box (from Outlook) however i cant send anything from my slackware box using Kmail.
When i send an email, Kmail tells me it has been sent but it just sits in the mail queue and doesnt go anywhere.
When i run mailq i get this:

(Deferred: Name server: example.com: host name lookup fa)

I have sendmail on this machine configured as a nullclient with the following as my sendmail.mc:

divert(-1)
include(`/usr/share/sendmail/cf/m4/cf.m4')dnl
OSTYPE(`linux')dnl
FEATURE(`nullclient', `mymailserver')dnl

Do i even need to be running sendmail at all on the client machine? If so what am i doing wrong?

Sendmail is a Mail Transfer Agent.

If you are sending a mail message all you need is an SMTP server to send through.

If you are delivering bulk mail or recieving bulk mail to/from domains, you need sendmail.

Your server running sendmail should suffice as the SMTP server.

Thanks for the reply.
Ive stopped sendmail on the client pc and ive configured Kmail to use 'SMTP' instead of 'sendmail' for sending messages (those were the two choices) and gave it my mail servers name and port 25.
Now when i try to send mail it gives me an error saying:

Sending failed
The sender address is missing

oh wait hang on...its working now
ignore the last post

WOOHOO!!!

great news.

Yes, ipop3 and sendmail I do believe are the listening protocols.

Using a mail client and USING SMTP or POP3 is the recieving application.