The problem now is that GMail is so big, it becomes "well your emails are being filtered in GMail so you need to fix it". With smaller providers it would be tha

The problem now is that GMail is so big, it becomes "well your emails are being filtered in GMail so you need to fix it". With smaller providers it would be that they were being too aggressive with email filtering. Fixing the problem is sometimes very hard with large providers as you really have nobody to contact for help or whitelisting. You can do all the best practices for sending emails (SPF, DKIM etc) but that will not help if you get filtered or blocked for some arbitrary and unknown reason. So for this reason people give up and either send their emails through well known mail senders or switch their users to services like GMail. This is sad as perhaps the last communications medium with open standards is being forced proprietary due to the difficulty in dealing with the large email providers. My company switched to GMail for our email, and Mandrill for sending out our mailing list although we have competent sysadmins.