Message says domain gmail.com is blacklisted?

This befuddles me somewhat. Any suggestions?

I just installed a blog with a contact form on my domain. Previously a static xsite pro site with virtually no traffic was there & no contact form to send an email.

Testing the contact form I got this in my gmail spam folder. The cc did not make it through my comcast.net addy at all. Site is on my host gator reseller account.

Message (I put in the x's):

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

xxxxxxx@comcast.net
SMTP error from remote mail server after MAIL FROM:<xxxxxxxt@gmail.com>:
host gateway.websitewelcome.com [A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

xxxxxx@comcast.net
SMTP error from remote mail server after MAIL FROM:<xxxxxxx@gmail.com>:
host gateway.websitewelcome.com [74.52.223.2]:
553 5.5.4 I was unable to send this e-mail because the domain ( gmail.com ) has been black listed due to spam or forgery.

]:
553 5.5.4 I was unable to send this e-mail because the domain ( gmail.com ) has been black listed due to spam or forgery.

Does this mean my mail server ip is black listed or my domain?

Thanks for any ideas,
Tom