Version:           4.7 (using KDE 4.7.1) 
OS:                Linux

This problem might be on the SMTP server side, but the setup worked in pre-Akonadi times. I just can't get it to work after the Akonadi switch.

It's a bit difficult to describe:

The german provider 1&1 provides several email adresses, let's call them "standard-mail@provider", "mail2@provider" and "mail3@provider" and so on. However, for all email adresses you have to use the same SMTP account where you authentificate with the user name "standard-mail@provider" and the corresponding password. 

Reproducible: Always

Steps to Reproduce:
That means in kmail I have set up the identities "mail2@provider" and "mail3@provider". For both I have, however, set up custom SMTP settings to use the 1&1 server and authenticate with "standard-mail@provider".

Actual Results:  
Whenever I try to send mail with one of those identities, a error popup says that the SMTP server rejects "mail2@provider" or "mail3@provider" as sender address ("invalid mail address"). However, for authentification purposes, the SMTP server should have been presented with the "standard-mail@provider" email address.

Expected Results:  
Mail sends flawlessly.