How to debug connection problems

Since installing KDE on my new system I've not been able to send mail
with Kontact.  I can read email fine.

I'd like to try to solve the problem, but I can't see how to get error
messages from kmail.  When I try to send a message there is no
message, but the email stays in the sent mail folder and doesn't get
sent.

I tried running kmail from the command line but no messages appear
when I try to send mail.

How can I debug the issue?  I'm quite stumped.

Thanks,

Michael