How MX Record Checking Works
When you submit a domain, the tool performs a DNS MX query to retrieve all Mail Exchange records associated with that domain. Each MX record contains two pieces of information: a priority value (also called preference) and a mail server hostname. The priority value is a number where lower values indicate higher preference, meaning the sending server should try the lowest-priority mail server first. The tool retrieves all MX entries, sorts them by priority, and then resolves each hostname to its corresponding IP addresses using A and AAAA record lookups for both IPv4 and IPv6 connectivity.
Beyond simple DNS retrieval, the checker performs connectivity validation by attempting to establish TCP connections to each resolved mail server on port 25, which is the standard SMTP port. This confirms that the mail servers listed in DNS are actually reachable and accepting connections. The tool also identifies the email hosting provider by matching MX hostnames against known patterns for major providers like Google Workspace, Microsoft 365, Zoho, ProtonMail, and others. If a domain has no MX records, the tool checks for an A record fallback, which is a legacy mechanism defined in RFC 5321 where the domain's A record itself acts as the mail server. Domains with neither MX nor A records cannot receive email at all.
When to Use This Tool
- Verifying email hosting setup — After configuring a new email hosting provider, check that the correct MX records have propagated in DNS and that priority values are set properly to ensure your primary server receives mail before any backup servers.
- Diagnosing undeliverable emails — If senders report that emails to your domain bounce with errors like "no MX record found" or "connection refused," use this tool to verify that your MX records exist, resolve correctly, and that the mail servers are accepting connections.
- Migrating email providers — When switching from one email host to another, use this tool to confirm that the old MX records have been replaced with the new ones and that DNS propagation is complete before decommissioning the old mail servers.
- Checking a domain before sending email to it — Before sending important business communications, verify that the recipient's domain has valid MX records and that their mail servers are online, which reduces the chance of bouncebacks and failed deliveries.
Understanding Your Results
The results display each MX record in a table showing the priority value, mail server hostname, resolved IP addresses, and connectivity status. Servers with the lowest priority number are your primary mail handlers. Most properly configured domains have at least two MX records for redundancy, so that if the primary server is unavailable, mail is delivered to the backup. If all MX records point to a single IP address or a single data center, the tool warns about the lack of redundancy, which creates a single point of failure for your email infrastructure.
The provider detection feature identifies which email platform handles mail for the domain, such as Google Workspace (indicated by MX records like aspmx.l.google.com) or Microsoft 365 (indicated by *.mail.protection.outlook.com). Connectivity results show whether each server responded on port 25 within the timeout period. A server that fails connectivity checks may be temporarily down, behind a firewall, or misconfigured. If the domain has no MX records at all, it either cannot receive email or relies on an A record fallback, which is generally considered a misconfiguration in modern email infrastructure. The tool also flags unusual configurations such as a null MX record (priority 0 with a dot as the hostname), which explicitly declares that the domain does not accept email.