MX Records Explained (Email Routing)

> MX decides where inbound email goes. If MX is wrong, your email can't arrive (even if your mailbox exists).

1) What MX does (simple)

MX records tell other mail servers which hostnames accept email for your domain.

2) Important rules

• MX points to a **hostname**, not an IP.
• The hostname used by MX must itself resolve (usually via an A record).
• If you have multiple MX records, the **lowest priority number is tried first**.

3) Priority and failover

A typical failover setup might be:

• MX 10 → primary mail server
• MX 20 → backup mail server

4) Common scenarios

A) Email hosted on your own server (example pattern)

• MX → `mail.yourdomain.com`
• A record: `mail` → your server IP
• Then add TXT records for SPF/DKIM/DMARC as needed.

B) Email hosted by a third party

• They provide MX targets (hostnames). You copy them exactly into your DNS UI.
• You should generally remove old MX records to avoid split delivery.

5) Trailing dot and DNS UI gotchas

• Some DNS providers automatically append your domain to values. Others expect a fully qualified hostname.
• If a provider expects a fully qualified name, it may look like `mx1.provider.com.` (note the dot).
• If you're unsure, follow the DNS UI examples and re-check the final saved value.

6) How to verify MX is correct

Checklist:

1. MX hostnames exist and resolve to IPs.

2. You don't have conflicting MX records from old providers.

3. Your receiving server is actually listening for inbound mail (and not blocked).

7) Common mistakes (and symptoms)

• MX points to an IP → inbound mail fails or behaves inconsistently.
• Mixed providers (some MX for one provider, some for another) → email randomly lands in different mailboxes.
• Firewall blocks inbound mail ports → senders get timeouts/bounces.

8) Best practices

• Decide *one* inbound email destination (one provider), then set MX accordingly.
• Add SPF/DKIM/DMARC after MX is correct (deliverability).
• Keep TTL moderate while changing, then increase later.

What to learn next

• Email Basics (How Email Works)
• SPF, DKIM, DMARC (Beginner)
• Creating Email Accounts (Plesk)