I'm having the same problem as fbengo (I'd love to hear if/how he solved the problem).
I've setup OST on hostek.com. Their support says they do not block any port out from a web app, so whatever the SMTP host supports will work.
I tried all ports my normal SMTP provider supports - 25,2500,25000 and 2501 and 463 if using SSL - no dice:
Failed to connect to smtp.fusemail.net
I then setup my own SMTP server on a windows server and opened a hole in our firewall to port 25 - I don't even see a failed or successful connection coming in for it and I get the same error as above.
If Hostek is correct in that they're not blocking SMTP traffic, what else could I have them check? Is there a PHP option that needs to be enabled for SMTP to work?