email-deliverability-audit

Email deliverability audit

Check the DNS of a sending domain, explain what is wrong and hand back records the user can paste into their DNS provider.

1. Look up the records

Check every domain the user sends from (the domain after @ in the From address, not the website if they differ). Look up these names, shown for example.com:

What	Name	Type
MX	example.com	MX
SPF	example.com	TXT, the record starting with v=spf1
DMARC	_dmarc.example.com	TXT
DKIM	<selector>._domainkey.example.com	TXT (often a CNAME to the mail provider)
MTA-STS	_mta-sts.example.com	TXT; the policy is at https://mta-sts.example.com/.well-known/mta-sts.txt
TLS-RPT	_smtp._tls.example.com	TXT
BIMI	default._bimi.example.com	TXT

Use whatever the environment allows:

• dig +short TXT example.com, dig +short MX example.com (or nslookup -type=TXT example.com).
• Without dig, DNS over HTTPS: curl -s -H 'accept: application/dns-json' 'https://cloudflare-dns.com/dns-query?name=example.com&type=TXT' (or https://dns.google/resolve?name=example.com&type=TXT). This sends the domain name to Cloudflare or Google.
• Without a shell or network access, ask the user to paste the records from their DNS panel.

A TXT value can arrive split into several quoted strings; join them before reading it.

SPF lookup count. SPF may use at most 10 DNS lookups (RFC 7208). Each include:, a, mx, ptr, exists: and redirect= costs one; ip4:, ip6: and all cost none. Follow every include: and redirect= target, read its SPF record and add its lookups to the total. Report the total and the include that adds the most.

DKIM selectors. A DKIM key sits under a selector the sender chose. If the user pasted message headers, take it from s= in the DKIM-Signature header. Otherwise try the common ones: google (Google Workspace), selector1 and selector2 (Microsoft 365), k1, k2, k3 (Mailchimp, Klaviyo), s1, s2 (SendGrid), zoho, zmail (Zoho), sig1 (iCloud), pm (Postmark), mandrill, amazonses, protonmail, default, dkim, mail, smtp.

• A record with an empty p= is a revoked key.
• Also look up a made-up selector such as zz-wildcard-probe._domainkey.example.com. If it returns a key too, the domain has a wildcard DKIM record and keys found under common selectors prove nothing.
• Finding no key under common selectors does not prove DKIM is missing; say so and ask for the header of a sent message.
• Key size: a p= value of about 216 base64 characters is a 1024-bit key, about 392 a 2048-bit key.

2. Explain the results

Lead with what blocks delivery, then what hurts it, then optional improvements.

Blocking (fix first)

• No SPF and no DKIM: major mailbox providers expect at least one on every message and reject or junk unauthenticated mail.
• More than one SPF record, or an SPF record that needs more than 10 DNS lookups: SPF returns permerror, which counts as a failure.
• +all in SPF: anyone can send as the domain.
• No DMARC record: required by Gmail and Yahoo for senders of more than 5,000 messages a day, and by Microsoft (Outlook.com, Hotmail) for high-volume senders.
• Null MX (0 .) on the From domain: replies cannot be delivered and receivers treat the domain as not sending mail.

Hurts reputation

• DKIM missing or only revoked keys: DMARC then depends on SPF alignment alone, which breaks on forwarding.
• DMARC without rua: no reports, so problems stay invisible.
• ?all or no all in SPF.

Optional

• DMARC p=none is the accepted minimum; recommend moving to quarantine and then reject after a few weeks of clean reports.
• MTA-STS and TLS-RPT protect inbound mail; BIMI shows a logo and needs DMARC at quarantine or reject.
• 1024-bit DKIM keys still work; 2048-bit is the current recommendation.

3. Give the fix as records

For each problem give the record type, host and value, ready to paste:

Type	Host	Value
TXT	@	v=spf1 include:_spf.google.com ~all
TXT	_dmarc	v=DMARC1; p=none; rua=mailto:[email protected]

Common SPF includes: Google Workspace include:_spf.google.com, Microsoft 365 include:spf.protection.outlook.com, Zoho Mail include:zohomail.com (or the regional variant shown in the Zoho admin). Take the exact include for any other service from that service's documentation instead of guessing. Keep one SPF record per domain and merge includes into it.

DKIM keys are generated by the mailbox provider (Google Admin: Apps > Google Workspace > Gmail > Authenticate email; Microsoft 365: Microsoft Defender portal, Email authentication settings, DKIM). Tell the user where to generate it; never invent a key.

4. Beyond DNS

Authentication is necessary but not sufficient. When the user's goal is inbox placement, add the checks DNS cannot show:

• Gmail and Yahoo bulk-sender rules: SPF and DKIM, DMARC aligned with the From domain, a one-click unsubscribe (RFC 8058 List-Unsubscribe-Post) for marketing mail, and a user-reported spam rate below 0.3% (aim for under 0.1%; monitor in Google Postmaster Tools).
• Sending servers need matching forward and reverse DNS (PTR) and TLS; mailbox providers such as Google Workspace and Microsoft 365 handle this for you.
• For cold outreach, send from a separate domain or subdomain than the main company domain, warm new mailboxes up gradually, keep per-mailbox daily volume modest, and verify lead lists before sending to keep bounces low.

Output format

1. One-line verdict per domain (for example "example.com: ready to send, 2 optional improvements").
2. Findings grouped as Blocking / Hurts reputation / Optional, each with the fix.
3. The DNS records to add or change, as a table.
4. What to re-check after DNS propagation (usually minutes, up to 48 hours).

If MailBeast is connected

If the MailBeast MCP server is available (tools such as list_mailboxes, get_mailbox), also check the sending side: run list_mailboxes to see each mailbox's status, health and warmup, and get_mailbox for the last error of any mailbox that is not healthy. Audit the domain of every connected mailbox. Learn more at https://mailbeast.ai.