Lock distribution list from outside mail

[amnz]

I want to protect a distribution list (all_employees@domain.com) to receive mail only from internal mailboxes.

Can this be done by using ACL? How? Is there a document/wiki page where ACL use in Zimbra is explained?

Thanks

[phoenix]

Search the wiki or the forums for the word 'restrict'.

[batfastad]

Yeah it's a real shame that you have to go through this pain...
RestrictPostfixRecipients - Zimbra :: Wiki
... to set this up

I'm one of the 224 people who've voted for this bug:
Bug 9620 – policy for who can send to a distribution lists