When the Mail Stops Flowing
There are few things more panic-inducing for an IT department than the phrase ‘we are not receiving any emails.’ While email delivery involves many moving parts, the DNS layer—specifically the MX records—is often the culprit. Troubleshooting delivery failures requires a systematic approach to identify syntax errors, routing loops, and priority conflicts in the zone file.
The ‘IP Address’ Trap
One of the most common and fatal mistakes made by junior system administrators is pointing an MX record directly to an IP address (e.g., 192.168.1.50). The RFC standards governing DNS and SMTP explicitly forbid this. An MX record must point to a valid hostname (an A or AAAA record), such as mail.example.com. If a sending server encounters an IP address in an MX record, it will typically abort the delivery attempt immediately, resulting in a hard bounce.
CNAME Conflicts at the Apex
Another frequent issue involves conflicts at the ‘zone apex’ (the root of your domain, like example.com). It is against DNS protocols to place a CNAME record at the zone apex alongside other records. If you place a CNAME at the root to redirect web traffic, it will override and break your MX records, completely halting inbound email. Web redirection at the root must always be handled via A records or ALIAS/ANAME records (depending on your DNS provider), never a CNAME.
Identifying Mail Loops
A mail loop occurs when an email is endlessly routed back and forth between servers without ever reaching a mailbox. This often happens in complex hybrid environments if the MX records point to a cloud filter, but the cloud filter routes the mail back out to a server that ultimately checks the MX records again, sending it back to the filter. Resolving this requires tracing the SMTP hops in the email headers. Always begin your troubleshooting by independently verifying what the global internet sees. Use our DNS Lookup tool to query your MX records, ensure they resolve to hostnames, and confirm the priorities are logically structured.
