OK, I'll bite. Don Gould wrote:
... Frankly I suspect that this may be pointless. I know that the shared server is used to host a number of applications that can be hacked (eg poorly written Joomla components) and used to leverage the sending of spam.
Your best course of action is probably to separate the email and Joomla services onto separate virtual servers and then update your acceptable use policy to include security considerations. Most system owners hold account owners responsible for all activity in their account regardless of whether or not that activity has been authorised by the account owner. This server has no business being on the internet, and I'm surprised that it can send email to anybody. While the public DNS black lists may not work quite like the Yahoo system, they both measure the reputation of your server, not your users and as such your legitimate users will be tarred with the same brush as the spammers. Cheers -- Lloyd Parkes