Kendo - 1:37 am on Apr 27, 2013 (gmt 0)
This is kinda related...
Yesterday I received abuse from someone who had received a support email from moi. His complaint was about the MailScanner warning in bold red letters about his beloved web site being a scam. Well I thought that we were sending and receiving via our own mail server that is a virtual hosted somewhere near New York. So I mistakenly assumed that it was his service using MailScanner. But this wasn't the case because we must have switched over to our local ADSL provider's service while the data center re-routed their network... and it was never changed back.
The point? Lots of IT professionals use their own mail servers and they can be hosted anywhere, perhaps in one of the "server farms" that you have blocked. Do you really think that rabidly blocking whole IP ranges is good for your business?