Although it does not appear to be officially documented, it is possible to subscribe to a Google Group without a Google Account. There are several ways to subscribe but, as I recently found out, Google Groups tries really hard to use a GMail account, if you have one. This post explains how to subscribe to a Google Group via email and how to avoid one pitfall that may result in messages being sent to your GMail address rather than the address with which you subscribed.
Recently I have been tinkering around with the Lift web framework and decided to subscribe to their mailing list, which happens to be hosted on Google Groups. After a quick search I found several sets of instructions for subscribing to a Google Group without a Google Account. Interestingly, many of the suggestions I found link to articles on Google Groups Help, none of which actually contain the by-email instructions. It is possible this was officially supported in the past and is now deprecated, but it continues to work nonetheless.
Undaunted, I followed the instructions and sent an email to email@example.com, then replied to the confirmation email it sent in reply. I received a “welcome to the group” message and everything looked good. Piece of cake, just like the good ol’ days. Then the list mail started flowing in to my GMail address. What!?
That’s odd, I thought. So I double-checked my sent folder (in Mutt) and confirmed that all messages were sent and received from my personal email address on this domain. I checked the server logs (did I mention that I host my own email?), all messages were sent through my mail server with the envelope sender set to my personal email address. How did Google Groups even get my GMail address?
A short bit more thought and I realized that my personal address was probably set as the backup/alternate email address for GMail, in case of the need to do a password reset. I checked, and indeed it was. That explains how Google associated the two accounts.
The easiest method that I could find to prevent Google Groups from sending emails to a GMail account is to make sure that the email address which is used to subscribe is not associated with any GMail account. If it is the backup/alternate address to a GMail account, remove it, then subscribe, then re-add it. That’s the best I could find.
If anyone can find an easier way to prevent this behavior, or a even a good explanation for why this Google Groups behavior is beneficial to anyone but Google, I’d love to hear it (and post it as a follow-up). Otherwise, good luck subscribing to a Google Group with your preferred email address.