Joining a google group (?) from a non-google email

I recently had the displeasure of needing to join a (non-usenet) google group. Google doesn't make this easy to find anymore, but they do allow you to subscribe from a non-google account. Each groups has a mailing list with an email address that looks like groupname@googlegroups.com, to which messages are sent. Subscription, then, can be achieved by emailing groupname+subscribe@googlegroups.com then replying to the confirmation message. (I don't think the confirmation link in the email does what you want.) It doesn't matter what is written in either email, except that the reply includes the subject line.

To unsubscribe, you can email groupname+unsubscribe@googlegroups.com, which google does advertise (including in the group's emails).