What happens when an A record points to the wrong IP?

You changed a server, migrated a host, or updated your infrastructure. Everything looks fine. But a day later, emails aren't arriving, connections are timing out, and nobody can figure out why. A misconfigured A record is one of the quieter culprits in email delivery failures because the error happens at the DNS layer, before any message is even sent.

An A record maps a hostname to an IPv4 address. When your MX record points to a hostname like mail.tidalpost.net, the sending server looks up that hostname's A record to find the actual IP to connect to. If that A record points to the wrong IP, the connection goes to the wrong place entirely.

Here's what actually breaks when that happens:

Connection failures. The IP at the other end doesn't respond, or it rejects the connection. From the outside, your mail server just looks down.

Wrong server reached. On shared hosting, an old IP might still belong to someone else's server. Traffic lands on a machine that has no idea who you are and drops the connection.

TLS certificate mismatch. Certificates are issued to specific hostnames. If the IP your A record resolves to doesn't match the certificate on that server, the TLS handshake fails. Sending servers that enforce encrypted connections will reject the delivery.

Complete mail delivery failure. Because MX records point to hostnames, not IPs, the entire delivery chain depends on that A record being accurate. A wrong A record on your MX hostname means incoming mail fails completely, not just partially.

Security exposure. In the worst case, the IP your A record points to is actively controlled by someone else. Traffic meant for your server gets intercepted. This is rare but real, especially after domain transfers or server migrations where DNS wasn't cleaned up properly.

To verify your A record is correct, run a quick DNS lookup from the command line. On Mac or Linux, use dig mail.yourdomain.com A. On Windows, use nslookup mail.yourdomain.com. The IP that comes back should match the actual IP of your mail server. You can cross-check by logging into your server or hosting panel to confirm the IP assigned there.

After any server migration or DNS change, give it time to propagate fully (usually a few hours, sometimes up to 48 hours), then run the check again. Cached DNS responses can make things look fine before propagation completes.

You can also check your broader DNS setup with our free Email Header Analyzer to spot mismatches after a delivery attempt, or use our SOS hotline if something is actively broken and you're not sure where to look.