As of June 2009, the latest stat I found, Gmail has 5.51% share of email users, 1/3 of either hotmail or yahoo mail. Definitely not "tens of percentage points."
http://www.campaignmonitor.com/blog/post/2839/email-client-p...
-14 karma · joined August 16, 2010
http://www.campaignmonitor.com/blog/post/2839/email-client-p...
Legitimate email providers take measures to ensure their customers aren't spammers and those who don't end up on the spammer lists and this is exactly the way it should be.
Until Google takes a stand against the spammers who use their systems, they should be on the list just like all the others.
If you are a company that provides spamming capabilities to anyone and everyone, then it is exactly valid to add them to a spam list.
You could say, "Plenty of legitimate users use gmail." Fine, maybe so, but if you are someone who uses gmail, you are surrounded by a cadre of spammers and should understand your credibility is instantly devalued.
Birds of a feather flock together. The solution is to stop using gmail.com.
A VERY VERY high percentage of spam in my inbox comes from gmail accounts. If tens of percentages points of spam is sent from a domain, then it's valid to add them to the list of spamming domains.