Email Tools

Mail Server Lookup

Look up a domain's mail server hostnames, IP addresses, and reverse DNS.

Enter a domain to look up its mail server hostnames, IP addresses, and reverse DNS.

More Email Tools

SMTP Connectivity Checker Email Security Summary DMARC Checker Email Header Analyzer DKIM Checker DMARC Record Generator SPF Checker

JustChecker tracks your mail server configuration continuously.

What Is the Mail Server Lookup?

It resolves each of a domain's MX hosts to its IP addresses and shows the reverse DNS name for each IP.

When to Use It

When setting up or debugging your own mail server.
To see which provider actually hosts a domain's email.

How to Use It

Enter the domain.
Review each mail host, its IPs and reverse DNS.

Understanding the Result

For self-hosted mail, each server's IP should have a reverse DNS name that resolves back to the same IP - many receivers treat mail without it as suspicious.

Limitations

This shows inbound mail servers. Outbound servers can be different - check which ones are allowed with the SPF Checker.

Example Result

MX host	IP address	Reverse DNS
`mail.example.com`	`203.0.113.25`	`mail.example.com`

Here the reverse DNS matches the hostname - exactly what receiving servers like to see from a self-hosted mail server.

Why Reverse DNS Matters

When your server sends mail, the receiving server looks up the PTR (reverse DNS) record of your IP. If there is none, or it is a generic name like ip-203-0-113-25.provider.net, many providers mark the mail as spam or reject it. The PTR record is set by whoever owns the IP - usually your hosting or VPS provider, through their control panel or support.

What the Hostnames Tell You

google.com hosts - Google Workspace.
outlook.com / protection.outlook.com - Microsoft 365.
zoho.com, secureserver.net (GoDaddy), hostinger.com and others identify those providers.
A security gateway such as Proofpoint or Mimecast in front of the real mailbox provider.

Check the MX priorities with the MX Record Lookup, test connections with the SMTP Connectivity Checker, and see the whole email setup with the Email Security Summary.

Frequently Asked Questions

Beyond just the MX hostnames, this resolves each mail server to its actual IP address(es) and reverse DNS hostname, giving a fuller picture of the underlying mail infrastructure behind your domain's MX records.

Many receiving mail servers check that a sending server's IP has a matching, legitimate-looking reverse DNS (PTR) record as a basic spam-fighting signal - a missing or mismatched PTR record can hurt deliverability even with otherwise correct SPF/DKIM/DMARC.

Often yes - the resolved IP addresses and reverse DNS hostnames frequently reveal a recognizable provider naming pattern (Google, Microsoft, or a dedicated mail hosting company), even without checking WHOIS separately.

This is normal for redundancy or load distribution across a provider's mail infrastructure, or if you have multiple MX records each pointing to a different physical server for failover purposes.

Not necessarily a fatal problem, but it's worth reviewing - some receiving servers weigh mismatched or missing reverse DNS more heavily than others when making spam-filtering decisions, so aligning it where you control the infrastructure is good practice.

No - WHOIS provides domain registration information; this tool resolves the actual technical mail server infrastructure (hostnames, IPs, reverse DNS) your MX records point to, which is a completely different layer of information.