We are currently using Zimbra with an SSL connection on SMTP. Over time we've found that it is very difficult to support (anti-virus programs hate it, some possible firewall issues, etc). We want to move away from it but at this point we have too many clients that are configured to use it that its not so easy to just turn it off, Is there any way to make TLS optional. For example, if the client requests an SSL connection, let them use it, if they don't accept it without SSL? Or even configure it on a domain by domain basis?