除了註冊 Google 帳號外，另外一個方式是透過 e-mail 直接登記。在這篇有人問到類似的問題：「How can I subscribe to a Google mailing list with a non-Google e-mail address?」。
不是 Accepted 那個答案，而是 c33s 給的答案：
Look for group email address in the heading of “Group email”, it will look like: Group email (Group Name)@googlegroups.com or visit the group web page on Google Groups, and click on “About this group”.
Send an email to (Group Name)+subscribe@googlegroups.com. +subscribe is the key, which is appended to the end of group’s email address. (Group Name) is the name of the group. Space is substituted by “-” (hyphen).
如果是 trac-announce 這個群組，就寄到 trac-announce+subscribe@googlegroups.com 這個位置，他會寄一封信回來確認，你把整封信回回去就可以了... (信裡有 auth key，寄回去就可以通過)
這個技巧在官方文件裡沒出現過... 但一直都是有效的 :o