While you are given “unlimited” email/cpu usage on a dedicated server, however, there are underlying restriction that is not commonly disclose before you signup. The following rules applies to most dedicated server (specific non virtual dedicated).
If your hosting provider receive spam complaints from an organization like AOL, SpamCop or others, they must take action to warn the customer about these complaints so they do not continue to occur.
The upstream provider will not allow hosting providers to host someone who receives continual spam complaints as this affects the entire IP network. A good hosting service provider do care about users having non-blacklisted email services, so, they must take action if they receive too many complaints for spam on any server.
Check out our list of good dedicated hosting services.