

Google Groups allows spammers to subscribe you to their groups in a workspace account, but doesn’t allow you to unsubscribe since you’re not part of that workspace account… Worse - all autoresponders for the spam will also be forwarded to all members of said group.
Since I do not participate in Google Groups, the nuclear option is to file all mails from Google Groups as spam with a Sieve script.
Note the require part may be too large as may sieve script also contains more rules than this one.
require ["body", "date", "editheader", "envelope", "fileinto", "imap4flags", "mailbox", "regex", "reject", "variables"];
if anyof(
header :contains "List-Subscribe" "groups.google.com",
header :matches "X-Google-Group-Id" "*"
) {
if header :matches "Subject" "*" {
set "subject" "${1}";
} else {
set "subject" "";
}
deleteheader "Subject";
addheader :last "Subject" "[Google-Groups-Spam] ${subject}";
fileinto "Junk";
}






They will be drowned in hundreds of „Thanks for your email, but we don’t do support via mail. Please open a ticket at $URL“ and „Thanks for your mail, we will get back to you shortly. Your ticket ID is #123456“. Also everything you add as an auto response will be distributed to all other victims in that group, so I chose to not be a dick.