Installing mailman3 on Debian bookworm with external mail postfix server

I would like to install mailman3 on my debian box (bookworm), but use an already existing postfix mail server on another host (can that be done?). I have the following settings in the mailman.cfg file in /etc/mailman3 [mta] # The class defining the interface to the incoming mail transport agent. #incoming: mailman.mta.exim4.LMTP incoming: mailman.mta.postfix.LMTP # The callable implementing delivery to the outgoing mail transport agent. # This must accept three arguments, the mailing list, the message, and the # message metadata dictionary. outgoing: mailman.mta.deliver.deliver # How to connect to the outgoing MTA. If smtp_user and smtp_pass is given, # then Mailman will attempt to log into the MTA when making a new connection. smtp_host: localhost smtp_port: 25 smtp_user: smtp_pass: # Where the LMTP server listens for connections. Use 127.0.0.1 instead of # localhost for Postfix integration, because Postfix only consults DNS # (e.g. not /etc/hosts). lmtp_host: 127.0.0.1 lmtp_port: 8024 I have SSH tunnels in place which make port 25 on the remote mail server available from my mailman server and port 8024 on my mailman server available on port 8024 on the remote mail server (if that's what's do be done - for the 2nd part, the port 8024, I am not fully sure if my understanding is correct). For some reasons, when starting mailman3, it tries to execute postmap which is installed on the mail server, but not on the mailman server. I guess, that this occurs because of the config file settings for incoming: and outgoing:. How can I change my configuration to get this setup working? Or (if this is not possible): How should I configure my system to have a new system running mailman3 connect to an already existing server running postfix. (What I probably should mention: The mailing lists should be for the mail domain which the existing postfix mail server is responsible for.)