MX lookup

Resolves the MX records and names the provider behind them — which decides whether an address on this domain can be checked before you send to it.

No MX means every address there bounces

A domain with no MX record cannot receive mail. This is the one case where a bounce is avoidable before sending, and it is worth checking a list for: one address in our last outreach batch was refused before it left because the domain had no mail servers.

Google Workspace and Microsoft 365 accept everything, then bounce

Both accept any recipient at SMTP time and decide afterwards, deliberately, so that addresses cannot be harvested by probing. No pre-send check can distinguish a live mailbox from a dead one on these providers. Measured rather than assumed: two addresses in our last batch sat on Google Workspace domains, passed every check we have, and hard-bounced. If your list is mostly Google-hosted, budget for bounces instead of trying to validate them away.

A typosquat has real MX of its own

gmail.com.com resolves mx203.inbound-mx.net and accepts mail. An MX check therefore says it is fine. We delivered an outreach email to it before noticing, which is worse than a bounce: the message reached a squatter and the status said delivered.

Other checks

  • SPF checkerReads the live SPF record, resolves every include it points at, and counts the DNS lookups. Over ten, receivers stop evaluating your SPF entirely.
  • DMARC checkerReads the record at _dmarc on your domain and explains the policy it publishes — including the cases where a record exists but does nothing.
  • Deliverability auditEvery check on this site at once, for a domain you are about to send from. It takes about a second and touches nothing but DNS.