Unfortunately, spammers like using free email domains to send their junk with. Hotmail, Yahoo, Gmail, Mail.com, Web.de, Mail.ru, Comcast et.c......Spambots are notorious for using these too. So many of the more popular ones get filtered out as possible spam immediately by other places.

When admining my games website, I have had to disable the automatic "posting" in the forums after registering. If I didn't, my forums would be filled with crap. So, through my Control Panel, I manually check through the new members listing to weed out possible spammers using hijacked legit emails. "CAPCHA" is not always full proof. I do have an email domain "ban list" of the more obvious ones. I still have not banned the legit ones because members of my own community use them.

Normally it's easy to tell a spambot/spammer from the name attached to the "email" but lately, they are getting sneakier and using "real" looking ones. Making my job weeding them out more challenging and forced to use other methods to check. Online "search" and IP traces do help track spammers back. But a lot of times, I have to use my "gut" feeling to confirm a new member and allow them to post in forums. Worked so far.

But larger sites either cannot afford this kind of personal "checking" or have to resort to "automatic" filtering using various means....and sometimes a legit email gets trapped and sent back. My regular Internet provider uses McAfee "Postini" that I subscribe to and my settings are up pretty high after a few incidents several years ago. So I make it a point to trawl through my Postini "filter site" regularily to check/pull out any legitimate emails from future or past customers.