Which users were affected?
Only GMass users who sent from a regular Gmail account, meaning an email address @gmail.com or @googlemail.com were affected. Google Apps users were not affected. The issue affected campaigns sent between 2016-07-11 18:28 GMT and 2016-07-14 04:00 GMT.
What exactly happened?
Yahoo has indeed been bouncing emails containing the shared tracking domain for GMass users with regular Gmail accounts (not Google Apps). Specifically, any email sent to an @yahoo.com address containing the domain gmss5.com bounced with this message:
Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain yahoo.com by mta5.am0.yahoodns.net. [188.8.131.52].
The error that the other server returned was:
554 Message not allowed – [PH01] Email not accepted for policy reasons. Please visit https://help.yahoo.com/kb/
This issue does not affect Google Apps users (those using Gmail but with their own company domain), because the shared tracking domain for Google Apps users is different than the shared tracking domain for regular Gmail users. The shared tracking domain assigned to Gmail users was blacklisted by Yahoo, thus resulting in the bounces.
What is a tracking domain?
For an explanation on what a tracking domain is and why it’s important for your email deliverability, please see this article on the issue of email blocking and this article on setting up your own tracking domain.
We have now resolved the issue by replacing the blacklisted tracking domain with a new tracking domain, but additionally, we have taken several other clean-up actions:
1. We have updated our reply management filters so that bounce like the sample above is categorized as a block instead of a regular bounce. GMass’s reply management system categorizes replies to an email campaign, and in this case, the message above indicates a block rather than a traditional bounce which means the email address is simply invalid.
2. Because previously the reply management system was treating messages above as regular bounces, it means that those @yahoo.com recipient addresses would have been added to the respective account’s Bounce list, therefore suppressing sends to that address in the future. Since the recipient address is actually valid, we have removed all affected @yahoo.com addresses from the GMass bounce tables. Approximately 6,000 yahoo.com email addresses (and addresses hosted by yahoo.com) have been deleted from the GMass bounce tables.
3. We have replaced the shared tracking domain used by Gmail users (www.gmss5.com), that was the cause of the Yahoo blocking, with a new tracking domain (which we won’t specify here).