Why do I get messages about "Implicit destination" from the mail manager?
John Reekie, 7 Aug 1999

MailMan tried fairly hard to trap mail that looks like spam. If a message comes in that doesn't look it is correctly configured, MailMan will hold it for approval, and send you (the list administrator) mail requesting that you approve or discard that message.

If you are forwarding mail from other lists or have aliases set up elsewhere to point to your list, then you will need to explicitly tell MailMan not to reject these messages. Go to the list administration page and select the "Privacy options" page. In the field labelled "Alias names (regexps) which qualify as explicit to or cc destination names", add the name of the forwarding list or alias that is sending to this list.

For example, if you have an alias foo-list@mymailserver set to point to a-gsrc-list@gigascale.eecs.berkeley.edu, then the configuration option for a-gsrc-list needs to have "foo-list" added to it.