I use this site to quickly find out where an IP is located.
http://whois.domaintools.com/61.152.170.42

Also, your domain should have an SPF entry in the domain's DNS if at all possible.
If the client is a company with lots of employees who use AOL, Gmail, Yahoo etc to send out usingHIDDEN@ccount@YourServer-com, that's not good.  They should all be using the 'authorized' mail server.
To setup an SPF record in your DNS, the instructions are at www.OpenSPF.Org
and if you get stuck, let me know.

Also, there are settings to limit the number of login attempts.  Our setting here is 5.
g_hacker_max in the Limits section of the SpamControl page is one of them.

BarryZ
Reading PA