Hi and thanks for helping out.
The mail server logs final lines say (nothing about the error 454 in the entire /var/log/mail.log):
Jan 4 10:15:24 Blacknight postfix/smtpd[21084]: cannot load Certification Authority data, CAfile="/etc/postfix/ssl/cakey.pem": disabling TLS support
Jan 4 10:15:24 Blacknight postfix/smtpd[21084]: connect from localhost[127.0.0.1]
Jan 4 10:15:24 Blacknight postfix/smtpd[21084]: warning: SASL authentication failure: cannot connect to saslauthd server: No such file or directory
Jan 4 10:15:24 Blacknight postfix/smtpd[21084]: warning: localhost[127.0.0.1]: SASL LOGIN authentication failed: generic failure
Jan 4 10:15:24 Blacknight postfix/smtpd[21084]: disconnect from localhost[127.0.0.1] ehlo=1 auth=0/1 rset=1 quit=1 commands=3/4
I don't know why the CAfile cant be loaded, the path seems correct. Is it a permissions problem maybe?
Any help is much appreciated
**Update**
I can send mail using telnet, which I asume proves it's something wrong with my settings in Roundcube.