I have a strange problem with Kmail in Mandriva 2010.2
It's a Kmail version 4.4.5
I set up the smtp server (Comcast) and all identities/accounts
I can receive email - no problem.
I cannot SEND email.
When I compose a message it all looks nice and when I click "send" button nothing happens. The Kmail just sits there and it wouldn't send the message.
When I try to close the message I tried to send it crashes the Kmail.
I get this error message:
The window "test message – KMail" is not responding. It belongs to the application kmail (Process ID = 10611, hostname = localhost).
Do you wish to terminate the application process including all of its child windows?
Any unsaved data will be lost.

That means kmail hangs, not good. First I'd suggest upgrading kmail, while staying in the 4.4 series (if you don't want to take the leap to akondified PIM). The 4.4.10 version is the last bugfix release for the old kdepim.

Does kmail detect correctly the server? By this I mean does it manage to get the configuration for SSL etc by itself (there's a button for that in the config).
Try a test run with a different smtp server, or maybe a clean config. I can't be much more help than this, because I've been using kdepim-4.8 for some time now, and it works quite a bit differently.

Serafean