Unless it's crashing with an error message saying it can't find the email server, then the email *is* sent.
Whether it arrives at its intended destination is a result of many factors:
- is the mailserver on your SSL server allowing that message through?
- is the receiving mailserver accepting the message? or is it dumping it in a blackhole because of some rule it doesn't like?
- sometimes those emails get dumped because they're tiny and only contain a few numbers, and have a subject line that's all capital letters, thus having the appearance of spam.
- sometimes emails get dumped because the mailserver configuration doesn't like the configuration parameters you've set. This is not uncommon when you have two separate servers for your website such as you've described for your SSL requirements.

You'll likely need to work with your hosting company to get them to follow the email through the server and find out what's happening to it.

If you're not seeing an error message on the screen or getting a blank white screen, then Zen Cart is under the impression that the email was sent successfully.