specific email blacklist on server

[WorkinOnIt]

I have a problem with an @gmail.com email spammer who has obviously worked out how to identify users on my server (probably from server DNS crosschecks I assume ). They are hitting each client's contact form and emailing each account on the server with very upleasant unsolicited spam.

Obviously I can't ban at the domain level, and it's not productive to ban at cPanel level -too many accounts.

What's the best way to set up a banned email blacklist in EXIM so I can stop this person harrassing the users on the server. Ideally I want a notification as root, but not the end of the world, I just want to block this spammer.

 

[ResellerWiz]

It sounds like an automated/scripted attack.

Have you considered simply adding captcha's to the contact forms?

 

[cPRex]

I also like the idea of a captcha. If it's a gmail.com address today, it could be outlook tomorrow, or Yahoo next week, so stopping the problem at the form level is the best solution.