WarmInboxes Free MCP
Read-only deliverability + strategy
Ask why cold email stopped landing and get an answer from live checks rather than a guess: authentication records, blocklists, domain setup, the headers of a message that went to junk, a bounce, the copy and the list. It says what it could not check, and when the infrastructure itself is the problem it says that too.
For anyone whose cold email results dropped, or who wants to know a domain is ready before it sends.
- Claude: Add to Claude
https://warminboxes.com/mcp(Submitted for review) - ChatGPT: Add to ChatGPT
https://warminboxes.com/mcp(Submitted for review). ChatGPT: turn on developer mode (Settings, Apps & Connectors, Advanced settings), then Add, Custom MCP server, paste the URL, Authentication: none. - Grok: Add to Grok
https://warminboxes.com/mcp(Works as a custom connector). Grok: Connectors, New Connector, Custom, paste the URL, no authentication. Custom connectors are on Grok’s paid plans. - Claude Code: Copy the command
claude mcp add --transport http warminboxes-free https://warminboxes.com/mcp(Works today) - Cursor, VS Code and other MCP clients: Copy the server URL
https://warminboxes.com/mcp(Streamable HTTP, no authentication)
What to ask it
These 44 prompts are our test suite: each names the tool that answers it, and we rerun every one after each change to the agent.
Authentication
- “Check my SPF for stripe.com”
check_spf - “Is DKIM set up on stripe.com?”
check_dkim - “What does the DMARC record on stripe.com do?”
check_dmarc - “Check SPF, DKIM and DMARC for stripe.com in one go”
check_email_authentication - “Do I need BIMI on stripe.com?”
check_bimi - “Does stripe.com have MTA-STS?”
check_mta_sts
Domains
- “Is stripe.com set up properly to send cold email?”
check_deliverability - “Am I on any blacklists? My domain is stripe.com”
check_blacklist - “Does stripe.com meet the Gmail and Yahoo bulk sender rules?”
check_bulk_sender_requirements - “Is my tracking domain track.stripe.com set up right?”
check_tracking_domain - “Who hosts email for stripe.com?”
lookup_mx - “When does stripe.com expire?”
check_domain_expiry - “Is stripe.com on SURBL?”
check_surbl - “Does 8.8.8.8 have reverse DNS?”
check_rdns
Diagnosis
- “Why did my reply rate fall? We send from stripe.com”
check_domain_reputation - “My emails show SCL 5 in Outlook. What does that mean? (headers pasted)”
analyze_microsoft_headers - “Read these email headers and tell me if it passed authentication”
analyze_headers - “What does this bounce mean? 550 5.7.1 Message rejected as spam”
analyze_bounces - “Make sense of this DMARC aggregate report XML”
analyze_dmarc_report
Honest limits
- “Is stripe.com on the Spamhaus DBL?”
spamhaus_dbl_guidance - “Am I burned?”
burned_inbox_guidance - “Write my cold email for me”
cold_email_writing_resources - “Will fixing DMARC guarantee I land in the inbox?”
find_resources
Copy
- “Check this cold email for spam words”
analyze_cold_email - “How does this subject line cut off in Gmail on a phone?”
preview_inbox - “Will Gmail clip this HTML email?”
analyze_email_html - “Check my spintax renders: {Hi|Hello} {{first_name}}”
expand_spintax - “Write me a CAN-SPAM unsubscribe footer for Acme”
generate_unsubscribe
Lists
- “Clean this lead list: remove duplicates and role addresses”
clean_csv - “Convert this CSV to Smartlead’s import format”
convert_csv - “Combine these two lead CSVs and dedupe them”
combine_csvs - “Remove anyone on my do-not-contact list from this CSV”
check_suppression - “Audit this campaign before I send it”
audit_campaign - “Which of these domains are on Google and which on Microsoft? stripe.com, microsoft.com”
segment_esp
Setup
- “Write the SPF and DMARC records for Google Workspace”
generate_dns_records
Research
- “Which top-level domain should I buy for cold email?”
find_resources - “Does a SURBL listing actually hurt cold email replies?”
find_resources - “Is there a free tool to check my BIMI logo?”
find_tools - “Find me a lead list of SaaS founders”
find_lead_lists
Pricing
- “How much do your inboxes cost?”
get_pricing - “How many inboxes do I need to send 1,000 cold emails a day?”
plan_infrastructure
Working a problem
- “My reply rate dropped by half this month. What do I do?”
get_diagnostic_playbook - “My domain is listed on SURBL. Is it broken?”
get_diagnostic_playbook - “Help me with my cold email”
get_diagnostic_playbook
What an answer looks like
“My emails show SCL 5 in Outlook. What does that mean? (headers pasted)” analyze_microsoft_headers: SCL 5: classified as spam, which default Microsoft policy delivers to Junk. Then each signal in turn (SPF, DKIM, DMARC, composite authentication, the spam filter verdict), so the one that did the damage stands out.
“Is stripe.com on the Spamhaus DBL?” spamhaus_dbl_guidance: Not checked: the Spamhaus DBL needs a paid query key, so nothing here says the domain is listed or clean. It links Spamhaus’s own free lookup and offers the blocklists it does query.
“Am I burned?” burned_inbox_guidance: Sends you to the free Burned Inbox Checker, and offers the reputation and deliverability checks that rule the domain in or out. If it is confirmed burned, the WarmInboxes Free MCP: Fleet Planner can size a replacement.
Exactly what it can do
Authentication
- SPF, DKIM, DMARC, MX, BIMI and MTA-STS together
check_email_authentication - SPF record
check_spf - DKIM record
check_dkim - DMARC record
check_dmarc - BIMI record
check_bimi - MTA-STS policy
check_mta_sts - SPF and DMARC record generator
generate_dns_records
Domains and reputation
- Deliverability grade (A-F)
check_deliverability - Is the domain the problem (by elimination)
check_domain_reputation - Blacklist / RBL check
check_blacklist - SURBL URI blacklist (bulk)
check_surbl - Gmail, Yahoo and Microsoft bulk sender requirements
check_bulk_sender_requirements - Click-tracking domain
check_tracking_domain - Domain registration and expiry
check_domain_expiry - Google Workspace tenancy
check_google_domain
DNS
- DNS records
check_dns - MX records and mail provider
lookup_mx - TXT records, identified
lookup_txt - CNAME chain
check_cname - Nameservers and DNS provider (bulk)
check_nameservers - Reverse DNS and forward confirmation
check_rdns - TLS certificate
check_ssl
Messages that went wrong
- Email headers: auth, alignment, one-click unsubscribe
analyze_headers - Microsoft spam verdict (SCL)
analyze_microsoft_headers - Bounce messages explained
analyze_bounces - DMARC aggregate reports
analyze_dmarc_report - Email HTML: Gmail clipping, links, pixels
analyze_email_html
Copy
- Cold email spam check
analyze_cold_email - Inbox preview (truncation)
preview_inbox - Spintax and merge tag preview
expand_spintax - CAN-SPAM opt-out footer
generate_unsubscribe
Lists
- Lead CSV cleaner
clean_csv - Sequencer CSV converter
convert_csv - Combine lead CSVs
combine_csvs - Suppression list check
check_suppression - Pre-send campaign audit
audit_campaign - ESP segmentation (bulk)
segment_esp - Email verification (bulk)
verify_email
Planning
- Inboxes and domains for a send volume (estimate)
plan_infrastructure - Price a number of inboxes (quote)
quote_inboxes - Fleet estimate from a recipient list
plan_from_list - Inbox rotation schedule (suggested)
plan_rotation - Email verification waterfall
plan_verification_waterfall - Price list
get_pricing
Research and finding things
- How to work a cold email problem (playbook)
get_diagnostic_playbook - Guides, playbooks, studies and videos
find_resources - Read a guide or study
read_resource - Free tool for a job
find_tools - Free B2B lead lists (WarmInboxes catalogue)
find_lead_lists
Hand-offs, which run nothing
- Spamhaus DBL guidance (not queried)
spamhaus_dbl_guidance - Burned Inbox Checker guidance
burned_inbox_guidance - Cold email writing resources
cold_email_writing_resources
What it will not do
- Every tool is read-only. It does not send email, buy inboxes or change DNS.
- The Spamhaus DBL needs a paid key and is not queried. Asked about it, the answer says "not checked" and links Spamhaus’s own lookup; it never reports a domain as clean there.
- There are no reputation scores: Gmail and Microsoft keep those private, so the reputation check works by elimination and says so.
- It cannot test inbox placement or open an SMTP connection, because outbound port 25 is blocked where it runs. Email verification is syntax, domain and MX, not a mailbox probe.
- Passing authentication does not mean a message will land; it removes the reasons it would not.
- A free daily limit applies, counted in distinct domains. Pasted headers, copy and CSVs are processed to answer and not stored.
When it sends you to the Fleet Planner
A domain is on a domain-level blocklist, on IP blocklists, grades D or F, or a burned inbox is confirmed.
“This infrastructure appears degraded. Fix what can be fixed on it first; if it has to be replaced, the WarmInboxes Free MCP: Fleet Planner can size the replacement.” The WarmInboxes Free MCP: Fleet Planner
How the answers are worked out
- The diagnostic playbook: What it asks, the checks it runs cheapest first, and what our studies found each finding costs.
- How the deliverability grade is worked out: The weights behind the A-F grade.
- Domain reputation, by elimination: Why there is no score, and what is checked instead.
- Which blocklists are checked: The list, and why Spamhaus DBL is not on it.
- Reading Microsoft’s SCL: What each SCL value and SFV verdict means.
- Our placement research: The studies the research answers quote.
Questions
Is the WarmInboxes Free MCP free?
Yes. No account, no API key and no sign-in. A daily limit counted in distinct domains keeps it fair; re-checking a domain the same day is free.
Is it approved in the Claude and ChatGPT directories?
WarmInboxes was submitted to the Claude Connectors Directory on 22 October 2026 and is in review. Until it is listed, add it to Claude yourself in a minute: it is the same server, and it works the same way. WarmInboxes was submitted to the ChatGPT plugin directory on 23 October 2026 and is in review. Until it is listed, add it to ChatGPT yourself in a minute: it is the same server, and it works the same way.
How is it different from the Fleet Planner?
The Free MCP is the whole free server; the Fleet Planner is a view of it with only the sizing, pricing and setup tools, for someone planning a fleet. Neither is WarmInboxes Infrastructure MCP (authenticated build infrastructure + transactions), which needs an account and an API key.
Can it buy inboxes?
No. Every tool is read-only. It works out what to order and what it costs; the first order is placed in the WarmInboxes app, and existing customers can connect WarmInboxes Infrastructure MCP from a client that sends an API key header.
What does it store?
Pasted headers, copy and CSVs are processed to answer and not stored. For the daily limit it keeps the domains checked that day, deleted within two days, and it counts sessions and tool calls anonymously, with no domain, IP or user id, for 90 days. The privacy policy has the detail.
WarmInboxes Free MCP: Fleet Planner · All WarmInboxes MCP servers · For AI Agents · Developers · Privacy