Your sendmail application allows the forging of headers (the From address in particular) which gets x10hosting on email blacklists for forging emails.
This is covered under the acceptable use policy here:
http://x10hosting.com/aup.php , specifically this part:
Internet Abuse
You may not engage in illegal, abusive, or irresponsible behavior, including:
[clipped a few reasons you didn't violate]
* Forging of any TCP-IP packet header or any part of the header information in an e-mail or a newsgroup posting
Because of this, that's why you had gotten suspended. What I'm not sure of is whether it's zero tolerance or not, so I'm leaving it here for the moment. From what I understand it's probably permanent with no access to the account or files, but that's for higher-ups to clarify.