Smtp 587 vs 465?

Hi,

I was setting up smtp on a sever of ours and noticed that when using port 465 with SSL - the connection timeouts and mail fails to send but if using port 587 the connection connects fine and mail sends. Any thought to why the connection using SSL fails/timeouts? Obviously I would prefer to use port 465 due to the secure connection.

Thanks for any advice/help. 

Cheers