Maybe this has been documented somewhere, but at least, I cannot find it on Google's own support pages. So here goes:
Google Groups have become a major mailing list hub. Unfortunately, Google tries to coerce people into using their web interface, which is something I object to for a number of reasons (it's ok to have it as a fall-back, but not as a primary interface). Now, Google Groups can be subscribed to using standard email, and here is how. As an example, I'll use the GitLab mailing list.
Figure out the list address:
- The group is at (https://groups.google.com/forum/#!topic/gitlabhq/). In that group, select a random posting, then use the button on the right of the "Sign in to reply" button to open a drop-down menu. Select "Show original".
Locate the "To: " line (maybe another line - see below). For this group, it should read
Subscribe to this group:
Use your email program to send an email to this address:
You will get a confirmation email with a token in the subject line. Reply to it.
You "should" get a welcome message, and be done.
I write "should", as sometimes, Google simply drops the email, and there is no way to figure out, why. Therefore, I tend to use email addresses which I already used in conjunction with Google - they work best.
HTH, and hopefully, Google will get their act together, one day.