How to resolve Microsoft Outlook not finding your new listserv domain name
If you are using Microsoft Exchange or Office 365, and add a custom domain name for your mailing list.
For example, listserv.example.com
Email sent to your mailing list may fail
When the email gets to MS Exchange / Outlook, the server does not look into the external DNS to find where to send the email.
Instead, it uses it's internal settings and decides there is no such address.
Check Accepted Domains and remove if found
Try sending email from Gmail or Yahoo or any other email account
Email sent from other accounts works just fine.
The problem is internal to MS Exchange / Outlook
Add a Contact pointing to the new listserve address
Mailing List <firstname.lastname@example.org>