Christian H. Kuhn via Mailman-users writes:

i got mailman-web up and runnung.

Is this a system package, or did you use the "Virtualenv install" (https://docs.mailman3.org/en/latest/install/virtualenv.html)?

Wanted to registrate the main user. Got an error ("Bei der Verarbeitung Ihrer Anfrage ist ein Fehler aufgetreten.").

Google says that means "An error occurred while processing your request." That's not a Postfix-like error message. Rather, that looks like a webserver. Did you try to register the "main user" in Postorius? Or in some web interface to your mail server?

What do you mean by "main user"? The site administrator, also called the superuser? I don't think you can register "the" superuser through the web.[1] You need to use

sudo -u mailman mailmanweb createsuperuser

or similar. (If you are using a system package manager rather than pip, it would usually prompt you to do this.)

In the logs of postfix, i could see the connection from mailman to postfix, but no mail was transmitted to postfix.

It's always helpful to post the full log message. If you're concerned about security/privacy, you can redact hostnames and mailaddresses (but say what was redacted, and be prepared to answer questions about the redacted text).

Did you send mail through a list? If not, why were you looking in the Postfix logs? It seems possible that some Mailman process raised an exception (a backtrace should be logged in error.log, mailmanweb.log or mailman.log), and tried to report to the site owner by email, but the address was unknown to Postfix.

Without more information it's hard to way what you need to do.

Regards, Steve

Footnotes: [1] Once you have a superuser, it is possible to create additional superusers. But it is not possible to do that for the first one.

-- GNU Mailman consultant (installation, migration, customization) Sirius Open Source https://www.siriusopensource.com/ Software systems consulting in Europe, North America, and Japan