The activation e-mail is missing

I tried to register to a community at Eine Gemeinschaft auswählen. I did not get the activation e-mail. I am using a Posteo.de e-mail address.

Hi! This forum is about the general software project Mastodon. Many independent users run and administer servers using the open source Mastodon software. To get help, you’ll need to contact the admin of the individual server you registered with—they’re the only ones who have access to the actual server that you registered on

Thank you very much for the answer!