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# MX Records (Mail Exchanger)
A Mail Exchanger (MX) Record is a type of Resource Record in the Domain Name System (DNS) that specifies the mail server responsible for accepting email messages on behalf of a domain name.
Without valid MX records, sending servers cannot locate your mail infrastructure, causing incoming emails to bounce or fail delivery.
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## How MX Records Work
When someone sends an email to `user@example.com`, the sender's mail transfer agent (MTA) performs the following steps:
1. DNS Lookup: Queries DNS for the `MX` records associated with `example.com`. 2. Priority Resolution: Sorts the returned MX hostnames by their preference (priority) number. 3. A/AAAA Lookup: Resolves the primary MX hostname to an IP address (`A` or `AAAA` record). 4. SMTP Connection: Attempts an SMTP connection to the primary mail server on port `25`. If the primary server is unreachable, it attempts to connect to secondary backup servers in order of priority.
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## MX Record Structure & Parameters
An MX record consists of three core components:
| Component | Value Example | Description |
| :— | :— | :— |
| Name / Host | `@` or `example.com` | The domain name receiving the email. |
| Preference / Priority | `10` | Integer value indicating server priority (lower numbers = higher priority). |
| Mail Server / Target | `mail.example.com` | The Fully Qualified Domain Name (FQDN) of the mail server. |
Crucial Rule: The target of an MX record MUST point to a valid domain name (`A` or `AAAA` record). It must never point directly to an IP address or a `CNAME` alias.
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## MX Record Priority Explained
Priorities allow domain administrators to set up primary and backup fallback mail servers.
```text Priority 10 : mail1.example.com ←- Primary Mail Server (Tried First) Priority 20 : mail2.example.com ←- Secondary / Backup Server (Tried if Priority 10 fails)
```
* Equal Priorities: If multiple servers share the same priority (e.g., two servers with priority `10`), incoming mail load is distributed between them (round-robin / load balancing). * Lower Number = Higher Preference: Priority `5` takes precedence over Priority `10`.
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## Example Configurations
### Example 1: Standard Self-Hosted Mail Server
| Record Type | Host | Priority | Value / Target | TTL |
| — | — | — | — | — |
| MX | `@` | `10` | `mail.example.com.` | `3600` |
| A | `mail` | — | `192.0.2.25` | `3600` |
### Example 2: Google Workspace Configuration
| Record Type | Host | Priority | Value / Target | TTL |
| — | — | — | — | — |
| MX | `@` | `1` | `SMTP.GOOGLE.COM.` | `3600` |
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## Common Issues & Troubleshooting
### 1. Pointing MX Records to CNAMEs
Pointing an MX record to a target that is a CNAME alias violates [RFC 2181 (Section 10.3)](https://datatracker.ietf.org/doc/html/rfc2181) and can lead to unpredictable mail loop errors or bounced emails.
### 2. Pointing MX Records directly to IP Addresses
MX records require an FQDN as their target. Pointing directly to an IPv4/IPv6 address will cause syntax validation failures across major mail servers.
### 3. Missing Trailing Dot (in Raw Zone Files)
In raw DNS zone files, failing to append a trailing dot (`mail.example.com.`) may cause DNS servers to append the root domain twice (`mail.example.com.example.com`).
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## Verification & Testing
You can test and verify your MX records using Telenegar Tools or terminal commands:
### Using Telenegar Tools
Validate your domain's mail exchanger configuration using [Telenegar DNS Check](https://wiki.telenegar.ir/doku.php%3Fid%3Dtools:dnscheck) or [Telenegar Mail Check](https://wiki.telenegar.ir/doku.php%3Fid%3Dtools:mailcheck).
### Using Terminal Tools
#### `dig` (Linux / macOS)
```bash dig +short example.com MX
```
#### `nslookup` (Windows / Cross-platform)
```cmd nslookup -type=MX example.com
```
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## Related Documentation
* [Telenegar DNS Check Tool](https://wiki.telenegar.ir/doku.php?id=tools:dnscheck) — Diagnostic tool for DNS record resolution and propagation. * [Telenegar Mail Check Tool](https://wiki.telenegar.ir/doku.php?id=tools:mailcheck) — Diagnostic tool for email authentication and mail server health. * [SPF (Sender Policy Framework)](https://wiki.telenegar.ir/doku.php?id=email:dns-configuration:spf) — Protect your domain against email spoofing. * [DKIM (DomainKeys Identified Mail)](https://wiki.telenegar.ir/doku.php?id=email:dns-configuration:dkim) — Add cryptographic signatures to outbound emails. * [DMARC](https://wiki.telenegar.ir/doku.php?id=email:dns-configuration:dmarc) — Define policy rules for SPF and DKIM alignment. * [Reverse DNS (PTR Records)](https://wiki.telenegar.ir/doku.php?id=networking:dns:reverse-dns) — Map mail server IP addresses back to domain names.
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