What MX records do
MX records tell the world which servers accept email for your domain. Each has a priority: senders try the lowest number first and fall back to higher ones. Equal numbers share the load. MX records only affect incoming mail — but they also tell us which provider you use, so the fixes elsewhere in the report can use that provider's exact values.
| If your MX hosts end in… | Your mail is hosted by |
|---|---|
google.com (e.g. smtp.google.com, aspmx.l.google.com) | Google Workspace |
mail.protection.outlook.com or mx.microsoft | Microsoft 365 |
zoho.com / zoho.eu / zoho.in | Zoho Mail |
protonmail.ch | Proton Mail |
messagingengine.com | Fastmail |
mail.icloud.com | iCloud+ custom domain |
mx.cloudflare.net | Cloudflare Email Routing (forwarding) |
pphosted.com / mimecast.com | A security gateway (Proofpoint / Mimecast) in front of your mailbox provider |
Problems we flag
- No MX at all. Senders fall back to the domain's A record, which is rarely a mail server. Replies and bounces get lost, and some receivers distrust senders whose domain can't receive.
- An MX host that doesn't resolve — usually a typo or a provider you left.
- An MX pointing to a CNAME, which RFC 2181 forbids. Most servers cope; some don't.
- Null MX (
0 ., RFC 7505) — a deliberate "this domain receives no mail". Good for domains that never send or receive, paired withv=spf1 -allandp=reject.
MX and sending rules
MX records don't authorise sending — that's SPF. A frequent mistake after switching providers is updating MX but leaving the old provider's SPF include (or forgetting the new one). Our full check compares them for you.
Questions
What does MX priority mean?
Lower numbers are tried first. If the server with priority 1 is unreachable, senders try the next-lowest. Servers with the same number share the load randomly.
Why does Google Workspace show one MX and older setups five?
Google now gives new setups a single record (smtp.google.com, priority 1). The older set of five aspmx.l.google.com hosts still works; you don't need to change it.
Can I send email from a domain without MX records?
Technically yes, but replies and bounces have nowhere to go, and some receivers treat it as a sign of a throwaway domain. Publish MX records for any domain you send from.
Do MX changes affect deliverability of my outgoing mail?
Not directly. Outgoing mail is authenticated by SPF, DKIM and DMARC. But changing providers usually means updating SPF and DKIM too, which is where things break.
Sources
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