Had this error after installing a new commercial certificate. The error seems valid as my server hostname and certificate name do not match, but it is my understanding this name mismatch is allowed and should still work.
To resolve this I just ran these two commands as Zimbra user.
zmlocalconfig -e ldap_starttls_required=false
zmlocalconfig -e ldap_starttls_supported=0
I am slightly concerned as to the security implications of disabling these settings. I am still on ldap not ldaps and this is on CentOS 7.