Well after upgrading our SSL configuration yesterday, it turns out that it seems there's still a few email clients out there that only support the old SSLv2 standard, the most notable one being chatteremail. Chatteremail is no longer being updated, but it's still a great IMAP client for older Palm phones and used by a lot of people.
Because of that, I've created a special hostname that can be used by users having problems with the upgraded SSL protocol. For those users, you just need to change your email software so rather than using
mail.messagingengine.com as the server name, you use
insecuressl.messagingengine.com instead. The name is explicitly messy to make sure that people realise this isn't a recommended hostname, it's only something to use if absolutely needed and it does carry security implications (SSLv2 has some known vulnerabilities)