MxToolbox Alternative: MX Lookup With SMTP Banner Check

• MX records sorted by priority, so you see which server receives mail first.
• SPF and DMARC: the domain's v=spf1 TXT record and the _dmarc record, shown raw.
• SMTP banner per MX host. The tool opens TCP connections to port 25 of every MX host in parallel and reads the greeting. The banner is parsed into product and version where the server advertises them, with a risk note for builds known to be outdated.

The same lookup works without a key from the command line:

curl "https://enterno.io/api/open/mx?q=example.com"

With an API key it is the mx tool in REST API v4, and check_mx over MCP.

• Blacklist checks. Its blacklist tool tests a mail server IP against over 100 DNS-based blacklists. We have no RBL check.
• Free blacklist monitoring. Its $0 plan includes weekly blacklist monitoring for one domain.
• Deliverability tooling. The Delivery Center plans ($129 and $399 a month) add inbox placement tests (30 or 100 a month), recipient complaint reporting, DMARC delivery reports, inbound and outbound mail-flow monitoring, BIMI management and domain impersonation protection.
• SuperTool. One input box for MX, DNS, blacklist and SMTP diagnostics, with links between results.

If mail is bouncing because your IP is listed, or you need DMARC aggregate reports read for you, use MxToolbox.

MxToolbox's API needs a key. Its API page says a free account gets a small daily quota of DNS requests and no network requests; blacklist lookups count as network requests, so they need a paid plan. Monitor queries also require a paid key.

On Enterno the MX lookup is free on the site, keyless through /api/open/mx, and available in REST API v4 on every plan, with 200 requests a day on the free Scout plan. Paid plans start at $5/month and add monitors and higher API limits; see pricing.

• No MX records. Senders then fall back to the domain's A record, which is rarely what you want. Publish at least one MX, or a null MX (RFC 7505) if the domain accepts no mail.
• MX pointing at a CNAME or an IP address. The MX target should be a hostname with its own A or AAAA record (RFC 2181 forbids an alias there); some senders reject anything else.
• A backup MX that is closed. If a lower-priority host never answers on port 25, the banner probe shows it, and you lose the fallback you think you have.
• Missing SPF or DMARC. Without them, receiving servers have less reason to trust your mail and more to file it as spam.
• Old mail server builds. A banner that advertises an outdated version tells attackers what to try; the risk note flags known cases.

• Email authentication check: SPF, DKIM and DMARC validated together.
• DKIM lookup for a specific selector.
• SMTP test: banner and STARTTLS on the port you choose.
• DNS lookup and DNS propagation after you change MX or TXT records.

For propagation tools, see our DNSChecker comparison.