[MM3-users] List mails blocked from GMX - web.de > Spamfolder

How can I configure Mailman3 so that Mails from the list will not be blocked by gmx.net I tried to send with the same user (mailman.cf) at my mail server, which will not be blocked by gmx. unfortunately, I get no bounce back message. They do just not appear in the mail folder of gmx.

At web.de they go to the SPAM folder.