How to add a Null MX to Plesk

Overview

Mail Exchange (MX) records define where emails should be routed to for a domain. This is a critical record for to you be able to receive email for your domain.

However, if you don’t have an MX record then according to RFC 5321 then remote mail servers will fallback to trying other records such as a CNAME or A record for the domain. While that may be handy in cases where the MX has been forgotten, unfortunately this also gives spammers an opportunity to try new locations to send emails to as well.

To block, we can create a “Null MX” record (defined in RFC 7505) which explicitly tells remote mail servers that no email will be accepted for the domain.

Instructions

1. Login into Plesk via the Conetix Control Panel.
2. Select the domain you wish to block all email for.
   Note: If you wish to block for all subdomains, select the primary domain
3. Go to Hosting & DNS -> DNS:
   
4. Add a new DNS record and set the type to MX:
   
5. If you wish to block for all subdomains, set the host entry to be *, set explicitly to a subdomain or leave blank for the current domain only.
   
   Ensure the Mail exchange server is left blank and set the priority to 0.
6. Ensure any other MX records have been deleted for that domain.
7. Click Update to save the changes to the DNS:
   
8. Once remote mail servers see the updated DNS, they should stop sending emails to the specified domain.