Version: 1.11.2 (using KDE 4.2.4) OS: Linux Installed from: Ubuntu Packages I think that you have problem in your e-mail check reg-exp. I have e-mail 2advance@my-site.com i can receive all mails from server. But when I'll try to configure sending from settings, KMail display notice that my mail "2advance@my-site.com" is not correct - I must enter another mail. So it doesn't allow me to send my mails from: "2advance@my-site.com"
This is the error message "The email address you entered is not valid because it does not seem to contain an actual email address, i.e. something of the form joe@example.org."
Cannot reproduce on 4.3 (KMail 1.12.0) so closing as the 4.2 track is closed. Please upgrade to the 4.3 version.