Mail catchall address for domain with LDAP users

[DavidePrincipi]

A domain without users has a complete list of valid addresses, known by Postfix DB, so it can reliably route unknown addresses to the catchall one.

Postfix does not directly connect to LDAP where users are listed. Without a complete list of available mailboxes it doesn’t know if an address corresponds to a user. Hence it cannot route the message to the catchall reliably.

This is the current UI, where the "Accept unknown recipients" switch is disabled for this limitation:

Proposed solution

• Configure Postfix to obtain the mailbox list from LDAP
• Make "Accept unknown recipients" setting indipendent from "Add users" checkbox
• Migrate the "Accept unknown recipients" setting from NS7 See Wrong migration of Mail's "Accept Unknown Recipients" setting #7257

Discussion

• (community) https://community.nethserver.org/t/accept-unknown-recipients-does-not-work/25443
• (private) https://mattermost.nethesis.it/nethesis/pl/5c1o46b1ijgnxcmxeur3fn3upe

[DavidePrincipi]

In Testing, Mail 1.7.0-dev.1

Create a domain and enable "Add user addresses from user domain" flag. Check the "Accept unknown recipients" option can be enabled and the catch-all recipient is saved and works correctly.

Test case 1

Check catch-all delivery when

1. The catch-all is a single user
2. The catch-all is a group of users

Test case 2

From test case 1, configure a forward for some catch-all recipient. Ensure the mail forward is honoured.