Whenever I try to send mail in kmail from my yahoo account (I paid for plus) it gives me an error message (readouts that display my email name, server it’s using, password and who is reciving it) and says that it will remain in my outbox until the problem is fixed. I have heard of people having this problem before, but they all seem to be dated from 2001 or 2004. And the fix they talk about (Yahoo doesn’t support sending mail to different @youremailcompany.com doesn’t sound legit. Nor will it send my yahoo account an email. At least that I know of. Anyways running 11.0 final KDE4. Most times I’m good at fixing these problems but this one is tough since I am just now trying to use email clients instead of online ones. And I want to stick with KDE apps. Also all my mail goes to the trash even if it’s good. So if anyone knows why that is thanks.
Compare your SMTP settings to this FAQ, you likely forgot to change the SMTP port, or enable auth.
see if this does not help you:
problem solved: Bug 161044 - SMTP SASL: no mechanism available (GMail+SSL)
I have a similar problem, but will only get to trying this solution this evening.