This week I had the issue that a customer with multiple mail domains was complaining that an incoming mail to a non-existing mail alias was accepted and was delivered to the user holding the existing mail alias.

Existing mail alias: ls@primarymaildomain.com
Non-existing mail alias: ls@maildomainalias.com

The incoming mail was accepted for both domains although we configured “Fullname only” in the configuration document of the server. We could not find the non-existing mail alias “ls@maildomainalias.com” in the Domino Directory.

After opening a case we received the following information from the development team:
we confirm that if the aliases are added to the parent domain, then mail gets delivered using the common name “ls”.

The issue was solved by creating a Global Domain document for every single mail domain and removing all alias domains from the documents:

After creating a single document for every existing mail domain ( thx a lot for having about 30 mail domains ) the incoming mail to the non-existing alias was not accepted by the Domino Server:

[27FC:000C-16E4] 07/28/2023 08:44:48 AM  SMTP Server: …. connected
[27FC:000C-16E4] 07/28/2023 08:44:48 AM  SMTP Server: Mail for ls@maildomainalias.com rejected for policy reasons.  Recipient could not be found in the Domino Directory.
[27FC:000C-16E4] 07/28/2023 08:44:48 AM  SMTP Server: …. disconnected. 0 message[s] received