[Geary] Can't add T-Online Account

[heebijeebi <heebijeebi gmx net>]

Hello Geary-Team,

today I wanted to add my T-Online Mail Account to Geary, but it won't work. I manually filled in all the fields and got the right values for IMAP/SMTP from the Mail Provider:

secureimap.t-online.de 993 SSL

securesmtp.t-online.de 465 SSL

But I always get an "SMTP Authentification Error". 

Adding and using my Gmail and GMX Accounts worked flawlessly but T-Online won't. Any ideas on how to fix this or what might be the problem here?

Thanks in advance!

Alex