I Laughed.

OK, this is probably the worst hosting company I’ve had to deal with.  They’ve got great T1 lines but lousy email hosting.  From their Knowledgebase:

If you attempt to send email and get an error message similar
to the following, then you are most likely NOT connected to the
Internet via One Communications
You need to use the SMTP server that is provided by your home
service. Be sure NOT to change POP settings.

Yes, that’s right.  SMTP only works if you’re directly connected to the server. The sad part is they don’t offer any residential services.  They’re strictly B2B.  And no one else has called them on it from what I gather.

UPDATE:  (7/2010)  It turns out they’ve updated their service to allow several different ways to send mail.  One includes using STMP-pop.server.com (I assume pop-before-smtp) and the other is using secure STMP and port 587.  Yay!
On a side note, it turns out there isn’t a 500 email/hour limit.  It’s completely arbitrary.  If they see traffic they don’t like…  No warning, just no mail for an hour (4 in our case).
Gah!