Symptoms
Unable to receive emails sent to a specific domain hosted on a Plesk server.
Cause
The affected domain doesn't have a valid DNS MX record/DNS MX record is missing or has no corresponding A DNS record:
# dig @8.8.8.8 +short -t MX example.com +short
10 mail.
# dig @8.8.8.8 +short -t MX example.com +short
(Empty Output)
# dig @8.8.8.8 +short MX example.com
mail.example.com
# dig @8.8.8.8 +short mail.example.com
Empty Output
Resolution
Note: It is required to wait for the DNS propagation period (up to 48 hours, but mostly faster).
If Plesk DNS server is used, add a valid MX/A record for the affected domain.
If DNS records are managed externally, add the appropriate MX records on the registrar's side.