New answers tagged google-groups
I'm years late, but I believe you can: Export mbox files from mailman. Import them into Thunderbird Use an IMAP connection to move the messages from your local Thunderbird set up to your gmail account. And then you'll be able to search like a pro.
I've looked in Gmail, Google Contacts, Google Plus and Groups and couldn't find this information. As a Google Apps Admin, however, I can lookup the user and see their groups from their User Account Page. If someone else has a better answer I would love to know as well.
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