Well… sending out bulk email to get people to join your site is spamming. You really don’t want to bulk email anyone that hasn’t specifically asked for it… through a double opt-in process.
Most likely, you didn’t get in trouble just for sending the mail… but because a large percentage of the people you sent it to considered it spam and reported it as such to Dreamhost. In that case, pretty much any host would terminate.
If you mean the mail was sent from non-DH servers, then that would make it look even more suspicious. That would basically be spamvertising your site, which is still spam related to your domain, regardless of where you sent it from. For example, if the recipients used spamcop.net to report it, it gives you the option to also report the site mentioned in the email, so those complaints still go to Dreamhost.
As far as the domain goes, that’s something you’d have to work out with Dreamhost. If you’re lucky, maybe they’ll let you pay the registration fee, then let you transfer it.
One thing’s for sure: You’ll want to be nice and patient with them if you want any chance of cooperation. Threats, repeat requests, etc… will likely lead to them just leaving things as is.
In any case, whether they re-activate your account, or you host elsewhere, be sure to read and fully understand the TOS. They’re usually pretty specific when it comes to defining what they consider spam.
Hope that helps!
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