Plesk Premium Email extension by Kolab is used in Plesk.
Non-default SSL certificate is set to secure mail traffic at Plesk > Tools & Settings > SSL Certificates > Certificate for securing mail;
Email traffic still uses Plesk Default certificate: How to verify that SSL for IMAP/POP3/SMTP works and a proper SSL certificate is in use;
/etc/dovecot/private/ssl-cert-and-key.pemfiles have different content:
# md5sum /etc/dovecot/private/ssl-cert-and-key.pem /etc/dovecot/private/dovecot.pem
This is a Plesk bug with ID PPPM-7808 which is planned to be fixed in future product updates.
for Kolab version 16.3.0 and earlier:
Connect to the server using SSH.
/etc/dovecot/private/ssl-cert-and-key.pemwith content from
# cp -f /etc/dovecot/private/dovecot.pem /etc/dovecot/private/ssl-cert-and-key.pem
for Kolab version 16.3.3:
Connect to the server via SSH.
Restart guam service:
# service guam stop
# service guam start
Note: as a workaround for Kolab version 16.3.2 upgrade to version 16.3.3.