mailman: duplicate list names/append domain name to list names

Mailman list names have to be globally unique.

Under Virtualmin > System Settings > Features and Plugins > Mailman > Configure, I have set “Append domain name to list names” to “Yes”.

With this option set to “Yes”, Mailman says subscribers should send messages to

But messages sent to that address are being rejected as follows:

Recipient address rejected: User unknown in virtual alias table

Postfix Mail Aliases lists an alias: > Program /usr/lib/mailman/mail/mailman post

Messages sent to are likewise rejected.

Why does this happen?