The problem is the 'standard' version of poptray doesn't support SSL (
AFAIK), you need a plug-in. There's an example of a POP3 SSL plugin on
this page - if that doesn't help then why not use the IMAP plug-in which does have SSL support? You will have to compile the plug-in, though. If you're only using poptray to check your new mail and then launch your mail client then it doesn't matter which protocol poptray uses.
If poptray doesn't suit you there are dozens of free mail checkers that support SSL, have a quick search on google.