Mail Server Lookup — MX Hosts with IPv4 Addresses

Sending MTAs look up MX for the recipient domain, sort by priority, and attempt delivery starting with the lowest number. Multiple equal-priority MX records load-balance. No MX means the domain may not accept mail unless A record fallback applies — increasingly rare.

Our lookup shows the same MX data senders use at SMTP time, plus IPv4 for network policy work.

Each servers entry includes priority, host, ips array, and raw MX record reference. primary is the first row after sorting — the preferred exchanger. summary states primary host, priority, and IPv4 count in plain language.

serverCount zero with summary about no MX means inbound mail may fail — confirm intentional null MX for send-only domains.

ips lists A record answers for each exchanger hostname. Empty ips with present host suggests DNS misconfiguration or propagation delay on the MX target name.

Allowlist maintenance uses these IPs in firewalls and SEG policies — re-run after MX migrations.

Cutover checklists compare live MX against vendor documentation. Priority 1 ASPMX.L.GOOGLE.COM patterns differ from Microsoft mail.protection.outlook.com clusters.

Snapshot MX before and after registrar changes; TTL on old MX may delay global sender behavior.

Higher numeric priority is fallback — tried when lower priority hosts are unreachable. Backup MX providers sometimes tarpit spam — presence in DNS does not prove acceptance policy.

Document which priorities are active production versus passive standby.

MX record lookup may show raw strings without IPv4 resolution. Mail server lookup adds ips for network teams. email-dns-health-check scores MX presence but not per-host IPs.

Pair with PTR record lookup on outbound sending IPs — orthogonal to inbound MX.

Domains that never receive mail may publish null MX (RFC 7505). serverCount may be one with special null target — interpret alongside organizational mail architecture.

Transactional senders still need SPF/DKIM/DMARC on the same brand domain.

GET /ip-tools/api/extended?action=smtp-server&domain=example.com returns servers, primary, serverCount, summary. Automate post-migration verification in runbooks.

Ingest primary.host and ips into CMDB when onboarding customer domains.

No SMTP banner grab, STARTTLS test, or greylisting behavior detection. Mail may reject at TCP 25 despite correct MX and A records.

Use port checker on MX IPs only with authorization — do not scan third-party infrastructure without permission.

MX and A records are public. Query domains you own or troubleshoot with authorization.

We do not permanently store lookups.