If you have recently installed or upgraded Thunderbird and now get the message “Login to server mail.uu.se failed” (Inloggningen till servern mail.uu.se misslyckades) when sending e-mail, and you are sure that you have entered the correct password, this solution will hopefully fix your problem.
As of Thunderbird 38, the default NTLM authorization protocol is NTLMv2 instead of NTLMv1. Uppsala University uses an Exchange 2010 server which appearently does not accept NTLMv2. To change this setting in Thunderbird you need to open the config editor (Tools -> Options -> Advanced -> Config editor) and change the setting for network.auth.force-generic-ntlm-v1 to TRUE.
The rest of the account settings should look like this: