MX Record Checker

MX (Mail Exchange) records tell other mail servers where to deliver email for your domain. When someone sends email to user@example.com, the sender's mail server looks up the MX records for example.com and connects to the mail server with the lowest priority number. If the primary mail server is down, it tries higher-priority-numbered servers. Each MX record has a priority (lower = preferred) and a hostname pointing to a mail server.

PTR records map an IP address back to a hostname. Mail servers use PTR records to verify that your mail server's IP resolves to a name matching its hostname (Forward-confirmed reverse DNS or FCrDNS). Without matching PTR records, many mail servers will reject your email or mark it as spam. Gmail, Outlook, and most corporate mail servers require FCrDNS. Your hosting provider or ISP controls PTR records for your IP — you must request them through their control panel.

MX priority (also called preference) is a number that indicates which mail server should receive email first. Lower numbers have higher priority — 10 is preferred over 20. When multiple MX records have the same priority, traffic is distributed randomly between them (for load balancing). A common setup: primary server at priority 10, backup server at priority 20. If the primary (10) is unreachable, senders try the backup (20). Setting up a backup MX provides redundancy if your primary mail server goes down.

If your MX record points to a hostname that has no A or AAAA record, your domain effectively cannot receive email. The sending mail server will fail to connect and the email will bounce. This typically happens when: (1) DNS records are misconfigured or incomplete, (2) you changed mail providers without updating all records, or (3) the mail server has been decommissioned. Fix by ensuring every MX hostname has a valid A record pointing to your active mail server IP.

A Null MX record (priority 0, hostname ".") explicitly signals that a domain does not accept email. This is used for domains that exist for web hosting or other purposes but should never receive email — like no-reply.example.com. Without a Null MX, senders may queue delivery attempts indefinitely. The Null MX tells senders to immediately reject email for this domain with a permanent bounce, preventing queue buildup. RFC 7505 standardizes this behavior.