My organization recently decided to update our Newsletter template that hasn't been changed in about 5 years. After developing and using Inbox Preview to make sure it looks good in Outlook, Gmail, Yahoo, etc. we started a 5% test on our mailing list. Over the last 2 weeks we've noticed an open rate differential of about 3% between our old template and our new template. On only 5% of our list we are getting about 1,000 less opens. So we could assume that if we sent this out to our whole list we'll get 20,000 less opens overall which is very significant to say the least. The email is converting very well in all other metrics; even better than the old template in most respects despite the open rate issues. It would seem that Inbox placement is the issue as Subject Lines and Preheaders are the same on the old template and the new template.

Is this something any of you have experienced? Were you able to find the cause? Is there a tool I can use to diagnose the reason for this? My gut says it has to do with Gmail's promotions tab. Could we really be getting a 3-5% open rate loss because of the Promotions tab? Has anyone here found a way to beat the promotions placement?