TLS Encryption Using SMTP VS and Connectors in Exchange 2003

I've been trying to configure TLS to work between my compaies exchange server and one of our clients. I've created a dedicated SMTP VS and associated IP and also an SMTP connector. I still cant get TLS to work and im banging my head against a wall here. It's also now messed up outbound mail to the two the client im trying to connect to as mail gets stuck in an outbound queue on my server and not delivering.

I'm pretty sure the certificates are setup correctly between the two sites as I can using OpenSSL use openssl s_client -connect www.xxx.yyy.zzz:2525 -starttls smtp
and view the cert details and then see the SMTP banner and list of commands including TLS, STARTTLS etc, but when I attempt a command, HELP for example it freezes and doesnt respond.

Has anybody got any ideas on this?

Thanks,

Patrick