MX records explained: the DNS record that decides where your email goes

Without an MX record, mail to your domain bounces. With the wrong one, mail gets delivered to a server you don't own. Here's how to read, write, and verify yours.

Modusdom Team · May 18, 2026 · 7 min read

MX records explained: the DNS record that decides where your email goes

MX records are the DNS instruction that tells the rest of the internet: "send email for this domain to these servers." If they're missing, your email bounces. If they're wrong, your email gets delivered to a server you don't control. Here's everything you need to know.

What MX stands for

MX = Mail eXchange. It's one of the resource record types in DNS, alongside A (address), CNAME (alias), TXT (text), and NS (nameserver).

When someone sends mail to you@yourbusiness.com, the sending mail server doesn't already know where your mail lives. It performs a DNS lookup on yourbusiness.com for MX records. The MX records reply with a list of mail server hostnames, ranked by priority.

What an MX record looks like

In DNS-text format:

yourbusiness.com.   MX   10   mail.modusdom.com.

Components:

yourbusiness.com. — the domain receiving the mail
MX — record type
10 — priority number (lower = higher priority, tried first)
mail.modusdom.com. — the hostname of the receiving mail server. The trailing dot indicates a fully-qualified domain name.

Multiple MX records and priority

Real domains usually have multiple MX records for redundancy:

yourbusiness.com.   MX   10   mx1.modusdom.com.
yourbusiness.com.   MX   20   mx2.modusdom.com.
yourbusiness.com.   MX   30   mx3.modusdom.com.

Sending servers try the lowest-priority number first (mx1), then escalate if that one is unreachable.

Priorities of the SAME number mean random load-balancing — either is fine.

Common provider MX setups

Google Workspace

yourdomain.com.   MX   1   smtp.google.com.

Google now consolidates to a single MX record. The older five-record setup (aspmx.l.google.com, alt1., etc.) is being phased out but still works.

Microsoft 365

yourdomain.com.   MX   0   yourdomain-com.mail.protection.outlook.com.

The hostname includes your domain (with dots → hyphens). Microsoft generates the exact value when you add the domain in M365 admin.

Modusdom Mailbox (OpenSRS Hosted Email)

yourdomain.com.   MX   10   mx1.hostedemail.com.
yourdomain.com.   MX   20   mx2.hostedemail.com.
yourdomain.com.   MX   30   mx3.hostedemail.com.

If you provision a mailbox through us, we set these automatically.

Hostinger Email

yourdomain.com.   MX   5   mx1.hostinger.com.
yourdomain.com.   MX   10  mx2.hostinger.com.

Common MX mistakes

1. Pointing MX to an A record's IP instead of a hostname

MX must point to a hostname (which then has its own A record), not directly to an IP address. The spec is strict about this.

2. Forgetting to remove old MX records

Switching from one provider to another? Delete the old MX records first. Multiple providers' MX records active simultaneously means mail randomly goes to whichever server answers first — usually the wrong one.

3. Hostname not resolving

The MX record points to a hostname that has no A record or doesn't exist. Sending servers can't connect, mail bounces. Always verify the hostname resolves: dig MX yourdomain.com then dig A <the hostname returned>.

4. Trailing dot confusion

Some control panels require the trailing dot (mail.modusdom.com.), others add it automatically. If you accidentally include it where the panel adds it, you get mail.modusdom.com.yourdomain.com — broken. If unsure, leave it off and let the panel normalize.

5. Catch-all MX for subdomains

An MX on yourdomain.com does NOT cover shop.yourdomain.com. If you want mail to x@shop.yourdomain.com, you need a separate MX record on the subdomain.

Verifying your MX records

Three quick checks:

Command line: dig MX yourdomain.com +short — returns the actual MX records being served.
Web tool: mxtoolbox.com — fast, free, shows MX + SPF + blacklist status.
Send a test: send yourself an email from a free Gmail/Outlook account. If it arrives within ~30 seconds, MX is working. If it bounces with "550 No such user" the MX is right but the mailbox doesn't exist; if it bounces with "host not found" the MX itself is wrong.

MX + SPF + DKIM + DMARC together

MX gets mail TO you. SPF, DKIM, and DMARC ensure mail FROM you doesn't get marked as spam. They're independent but related — both need to be configured for a reliable email setup.

If you use Modusdom Mailbox, we set all four (MX, SPF, DKIM, DMARC) automatically. If you bring your own mail provider, follow their setup guide for each, then verify with mail-tester.com.