MX Lookup

What are MX Records?

MX (Mail Exchanger) records are a type of DNS record that tells the internet where to deliver email for your domain. When someone sends an email to [email protected], their mail server performs a DNS lookup to find the MX records for yourdomain.com. The result tells it exactly which mail servers are responsible for accepting email on your behalf.

Each MX record consists of two parts: a priority number and a mail server hostname. The priority number determines the order in which mail servers are tried. A lower priority value means the server is preferred — for example, a server with priority 10 is tried before one with priority 20.

Most domains have multiple MX records to provide redundancy. If the primary server is unavailable, the sending server automatically falls back to the next server in the priority list. This ensures email delivery continues even during maintenance windows or outages.

How to Read MX Results

Our MX lookup tool provides several data points for each mail server:

• Priority — Lower numbers indicate higher preference. Servers with equal priorities share the load through round-robin delivery.
• SMTP Banner — The greeting message returned when connecting to port 25. This often reveals the server software (e.g. Postfix, Microsoft Exchange, Google SMTP) and confirms the server is actively accepting connections.
• Response Time — How quickly the mail server responded to the SMTP connection. Times under 500ms are excellent, under 1000ms are normal, and above 2000ms may indicate server load or network issues.
• IP Addresses — The resolved A records for the mail server hostname. Multiple IPs indicate load balancing or geographic distribution.
• Status — Whether the server is reachable and responding on SMTP port 25. An "Unreachable" status does not necessarily mean the server is down — firewalls or rate limiting may block test connections.

Common MX Issues

• No MX records found — The domain cannot receive email at all. This could mean the domain is not configured for email, or the DNS records were accidentally deleted.
• Unreachable mail servers — If all MX servers are unreachable, incoming email will be deferred by the sender and retried over hours or days. If servers remain down beyond the retry window (typically 5 days), the email bounces permanently.
• Misconfigured priorities — Having all servers at the same priority when they should have a hierarchy, or assigning the wrong priority to backup servers, can lead to unbalanced load or email being delivered to the wrong server.
• Single point of failure — Domains with only one MX record have no failover. If that server goes down, all inbound email is lost or delayed until it recovers.
• MX pointing to a CNAME — MX records must point to an A record hostname, not a CNAME. While some servers tolerate this, it violates the RFC standard and can cause unpredictable delivery failures.

Why MX Records Matter

MX records are the foundation of email delivery. Without correctly configured MX records, your domain simply cannot receive email. For businesses, this means lost customer enquiries, missed invoices, and broken communication workflows. Properly configured MX records with redundancy ensure that your email keeps flowing even when individual servers experience issues.

Beyond basic delivery, MX configuration also affects email performance. Geographically distributed mail servers reduce latency for senders in different regions, and load-balanced priorities prevent any single server from becoming a bottleneck during high-volume periods.