sslv3 alert bad certificate when attempting to connect with Mail Client

Question

I have a Debian vServer with a pre-installed Froxlor. Froxlor uses Dovecot and Postfix for mailservers. I set up 1 catchall email address which forwards all messages to my private mail. This is all working.

Connecting to the account with a mail client like Thunderbird would not work though. I installed my SSL certificate and private key following the instructions given in this tutorial

According to SSl-Check Websites my certificate seems to be alright.

/var/log/mail.log

Aug 24 10:18:10 mysvr dovecot: pop3-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=1.1.1.1, lip=1.1.1.2, TLS: SSL_read() failed: error:14094418:SSL routines:SSL3_READ_BYTES:tlsv1 alert unknown ca: SSL alert number 48, session=<nsg7kNiQ5ABfWuR6>
Aug 24 10:18:10 mysvr dovecot: pop3-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=1.1.1.1, lip=1.1.1.2, TLS: SSL_read() failed: error:14094418:SSL routines:SSL3_READ_BYTES:tlsv1 alert unknown ca: SSL alert number 48, session=<Ou49kNiQ/QBfWuR6>
Aug 24 10:18:12 mysvr postfix/smtpd[26083]: connect from ip52525.dynamic.myisp.com[1.1.1.1]
Aug 24 10:18:12 mysvr postfix/smtpd[26083]: improper command pipelining after EHLO from ip52525.dynamic.myisp.com[1.1.1.1]: QUIT\r\n
Aug 24 10:18:12 mysvr postfix/smtpd[26083]: disconnect from ip52525.dynamic.myisp.com[1.1.1.1]
Aug 24 10:18:12 mysvr dovecot: imap-login: Aborted login (no auth attempts in 0 secs): user=<>, rip=1.1.1.1, lip=1.1.1.2, session=<84JckNiQ8ABfWuR6>
Aug 24 10:18:13 mysvr dovecot: imap-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=1.1.1.1, lip=1.1.1.2, TLS: SSL_read() failed: error:14094418:SSL routines:SSL3_READ_BYTES:tlsv1 alert unknown ca: SSL alert number 48, session=<oFdnkNiQ5ABfWuR6>
Aug 24 10:18:13 mysvr dovecot: imap-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=1.1.1.1, lip=1.1.1.2, TLS: SSL_read() failed: error:14094418:SSL routines:SSL3_READ_BYTES:tlsv1 alert unknown ca: SSL alert number 48, session=<QvRokNiQ+wBfWuR6>

Solution

The problem is dovecot's

10-ssl.conf

This file only accepts *.pem files and NO *.crt files