Here's what someone else with the same problem posted and got for a reply. Please follow bulk sender guidelines attached below. Go through the security checklist of Google: mail.google.com/support/bin/static.py?page=checklist.cs&tab=29488 Click here Set up 2-step verification for your account: www.google.com/support/a/bin/answer.py?hl=en&answer=175197 Click here For further issue, please post your query in Gmail help forum: www.google.com/support/forum/p/gmail?hl=en Click here Hope this helps.