I think that someone (one of my hosting clients) is using my server for sending spam, and Hotmail blocked my server: i can't telnet to mx*.hotmail.com and any mail I try to send to Hotmail is blocked.

I have two questions:

a) How can I know WHO is sending that spam? I'm using CPANEL/WHM

b) How can I unblock my server in Hotmail so I can send mail to hotmail accounts?

Thanks!

You may need to contact them to figure out what started it all. It is pretty much impossible to track who was spamming in the past you need to look for it in the future. I would suggest turning on the x-spam headers as closely monitoring the box.

It is also possible that hotmail blocked you because too many users clicked "this is spam" from emails coming frmo your server even if they were legit.

Also check you have a proper PTR record for your server.

Also google your IP and see if you are on any spamlists which may have some information.

Well, I googled and searched on many "blacklists", and my server is NOT on them. The problem is ONLY with hotmail.com. Even yahoo.com works correctly.

What else can I do? Do you know where to contact Hotmail?

BTW, my IP is 209.85.7.40

Thanks!