How to subscribe to a Google Group with a custom email address

The interface of Google Groups implies that you can only subscribe with a Google Account and its email address. But even Google makes it harder than it should be, it is possible to use any other valid email address to subscribe. You just have to call the subscription page manually by editing a URL:

http://groups.google.com/group/name-of-the-group/boxsubscribe?email=your-url-encoded-email-address

Just substitute the following:

• name-of-the-group → the group you want to subscribe to
• your-url-encoded-email-address → your url-encoded email address