[Mailman-Users] Too much rejects from gmail.com recipient

Hi,

A user on one of my hosted mailing lists just received a message which said he must confirm is registration, after too much rejects, before cancellation of his registration. He has a gmail mailbox (I don't know if it's matter). And maybe it is not alone :(

I have send email from my server to my personnal gmail mailbox with succes, and a test on www.mail-tester.com give my 8/10 You can see the result here : http://www.mail-tester.com/web-KUfidY

I don't have DKIM authentification on the mailman server, and I don't know if it's possible to set it up.

Else, I don't have any idea how to solve the problem :(

Hedy