WarmInboxes Free Deliverability Tools

Connect it to your AI

Claude Code

claude mcp add --transport http deliverability-tools https://warminboxes.com/mcp

Claude, ChatGPT, Cursor and other apps

Add it as a custom connector with this URL (Streamable HTTP):

https://warminboxes.com/mcp

Cursor, VS Code and other apps (mcp.json)

{
  "mcpServers": {
    "deliverability-tools": {
      "url": "https://warminboxes.com/mcp"
    }
  }
}

Tools it offers

52 tools, as the server itself reported during our check on Oct 31, 2026.

• check_deliverabilityGrade a domain A-F for cold email readiness. Checks SPF, DKIM, DMARC, MX, blacklists and domain age together and returns a weighted score with a per-check breakdown and what to fix. Start here for open-ended "is this dom
• check_spfLook up a domain's SPF record and validate it, including the recursive DNS lookup count that silently breaks SPF past 10.
• check_dkimFind and validate a domain's DKIM signing key, including key strength. Leave selector empty to auto-scan 26 common selectors (google, selector1, k1, and the rest). When no key is found, reports whether the selectors are
• check_dmarcLook up and parse a domain's DMARC record: policy, subdomain policy, percentage, alignment and reporting tags, each explained. p=none (monitoring) passes: it meets Google and Yahoo's requirement and is fine for broad col
• check_bimiValidate a domain's BIMI record, the logo SVG, the VMC, and the DMARC enforcement level Gmail requires before it will show a brand logo.
• check_mta_stsValidate a domain's _mta-sts DNS record and its published policy file: mode, MX patterns, max_age and TLS-RPT.
• check_sslRead a host's TLS certificate: issuer, validity dates and days remaining, subject alternative names, key type and size, signature algorithm, chain, negotiated protocol and whether the chain is trusted and covers the host
• check_dnsQuery any DNS record type for a domain: MX, TXT, A, AAAA, CNAME, NS, SOA, CAA.
• lookup_txtEvery TXT record on a domain, with each one identified (SPF, DKIM, DMARC, MTA-STS, TLS-RPT, BIMI, or which service's ownership token it is), plus the four underscore names a receiver reads — _dmarc, _mta-sts, _smtp._tls
• check_rdnsThe PTR record for an IPv4 or IPv6 address, and the forward lookup that decides whether it counts. Reverse DNS is delegated to whoever holds the address block, so a PTR alone proves nothing — the operator of an IP can po
• check_blacklistCheck a domain or IP against 20+ major email blacklists (Spamhaus, Barracuda, SORBS and others) and report which list it appears on.
• check_surblCheck domains against the SURBL URI blacklist in bulk. URI blacklists list the domains that appear inside a message body, so a listed tracking or landing domain sends the whole email to spam however clean the sender is.
• check_nameserversGet the NS records and the DNS provider behind one domain or a whole list. Useful for working out who actually controls a domain's DNS before trying to fix its records.
• check_domain_expiryGet a domain's registrar, creation date, expiry date and days remaining, over RDAP with a WHOIS fallback for ccTLDs that publish no RDAP service. Domain age is one of the strongest cold-email risk signals.
• check_google_domainTell whether a domain is already attached to a Google Workspace account, or is clear for a fresh Google tenant.
• check_cnameFollow a host's full CNAME chain and flag the mistakes that break a cold-email tracking domain. Pass expected to assert where the chain should end up.
• verify_emailCheck email addresses for syntax, live MX records, disposable providers and role prefixes (info@, sales@). Does not open SMTP connections, so catch-all domains come back valid.
• lookup_mxLook up a domain's MX records with priorities and resolved IPs, and identify the mailbox provider (Google Workspace, Microsoft 365, Zoho, Fastmail and others) and any security gateway in front of it (Mimecast, Proofpoint
• segment_espSplit a list of domains by the email provider behind them (Google, Microsoft, a security gateway, or another provider) from their MX records. WarmInboxes routes Google-hosted recipients to Google Workspace inboxes and ev
• plan_from_listEstimates a sending fleet for a recipient list. Looks up the MX records of up to 100 recipient domains (or addresses) to measure the provider mix, then sizes a Google Workspace pool for the Google-hosted recipients and a
• plan_infrastructureEstimates how many inboxes and domains a daily cold email volume needs and the monthly cost at WarmInboxes' published prices. Inputs: emailsPerDay; optionally the provider (esp), prewarmed or fresh, billing cycle, emails
• quote_inboxesPrices a given number of inboxes at WarmInboxes' published prices: the domains (or Azure tenants) they sit on, daily sending capacity at the provider's pace, monthly cost and delivery time. Use it when the person already
• get_diagnostic_playbookReturns WarmInboxes' diagnostic playbook for a cold email problem: the questions to ask the person, the checks to run in order from cheapest to most expensive (with the tool for each), what WarmInboxes' published studies
• expand_spintaxExpand a spintax template such as "{Hi|Hey} there" and render its Liquid merge tags, returning the total number of variations, every variable the template references, any variable with no value and no default, and a set
• generate_unsubscribeBuild a CAN-SPAM and GDPR compliant opt-out footer in plain text and HTML, with a checklist saying which compliance requirements the details given actually satisfy. A footer with no postal address is the usual failure.
• check_email_authenticationSPF, DKIM, DMARC, MX, BIMI and MTA-STS for one domain in one call, each judged pass, weak, fail or not set, with the essentials separated from the optional records. BIMI and MTA-STS are optional and come back "absent", n
• check_domain_reputationFor "this domain used to land and now it does not". Checks the domain against SURBL, its authentication, its age and the address its website resolves to, and returns a verdict by elimination (listed, broken, young, clean
• check_tracking_domainCheck the domain a campaign's tracked links point at: whether it resolves, serves a valid certificate, is listed on SURBL, sits on a listed address, belongs under the sending domain, and whether it is a platform's shared
• check_bulk_sender_requirementsThe bulk sender requirements, sorted honestly: SPF, DKIM, DMARC and MX checked from DNS; forward and reverse DNS when given the sending IP; one-click unsubscribe and From alignment when given a received message's raw hea
• analyze_headersRead a received message's raw headers. Returns the SPF, DKIM and DMARC verdicts the receiver recorded, which domains authenticated and whether they align with the From domain (why DMARC failed on a message that "passed")
• analyze_email_htmlRead an email's HTML. Returns its size against Gmail's ~102 KB clipping limit with what is taking the room, every link and image host, tracking pixels, URL shorteners, and each linked domain checked against SURBL. Parsed
• analyze_dmarc_reportRead DMARC aggregate (rua) reports and say who is sending as the domain and what fails: messages passing and failing, failures that are alignment only, quarantined and rejected counts, and each sending IP with its SPF an
• analyze_cold_emailScore a cold email's copy 0-100 for spam risk before it is sent: weighted trigger words by category and severity (subject hits weigh extra), ALL-CAPS, links and shorteners, currency and percent-off offers, obfuscated spe
• audit_campaignAudit a cold email campaign before launch: the lead CSV and the sequence checked together for merge tags with no column or empty values, variable syntax the sequencer will not parse, role and disposable addresses, duplic
• analyze_bouncesClassify bounce messages (NDRs): invalid address, full or disabled mailbox, reputation block, authentication failure, throttling, content block or configuration, each with whether it is hard, soft or a block, why it happ
• analyze_microsoft_headersRead the spam verdict Microsoft 365 or Outlook stamped on a delivered message: SCL (spam confidence), BCL (bulk), PCL, SFV, the category, and the SPF, DKIM, DMARC and composite authentication results, each explained. Use
• preview_inboxShow how a cold email's sender name, subject line and preview text are cut off in Gmail desktop, Gmail mobile and Outlook, with warnings (no sender name, all caps, empty preview, etc.). Use it to check a subject line fit
• generate_dns_recordsWrite an SPF record from the providers that send for a domain (with an estimate of its DNS lookups against the limit of 10), a DMARC record from a policy, and where a provider publishes DKIM. Returns host, type and value
• plan_rotationSuggests a two-batch inbox rotation schedule: the fleet split in half, one batch sending while the other rests, swapped every 1, 2 or 4 weeks. Returns batch sizes, the daily load per active inbox compared with a 15-a-day
• plan_verification_waterfallPrice an email verification waterfall: the list run through verifiers in sequence with unknowns passed down the chain, every order compared, cheapest cost per usable email first. Uses typical figures for three verifiers

Questions