ChatGPT plugin
WarmInboxes for ChatGPT
A ChatGPT plugin for cold email: check whether a domain is ready to send, score a draft for spam triggers, clean and convert lead lists, read why a message went to junk, size the inboxes a volume needs, and quote our own placement research. Free, read-only, no account.
Submitted for review
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.
Add it to ChatGPT
Custom MCP servers need developer mode, on the ChatGPT plans that offer it.
- Turn on developer mode in ChatGPT: Settings, Apps & Connectors, Advanced settings. ChatGPT only accepts custom servers with it on.
- Click Add to ChatGPT. ChatGPT opens on Plugins, and the server URL is copied.
- Click Add, choose Custom MCP server, and fill it in with the values below. Authentication: none.
- In a chat, add WarmInboxes from the tools menu and ask, for example, "Is stripe.com set up properly to send cold email?"
- Name:
WarmInboxes - Description:
Free cold email deliverability checks - MCP server URL:
https://warminboxes.com/mcp - Authentication:
No authentication
What to ask it
Domains
- “Is stripe.com set up properly to send cold email?”
check_deliverability - “Check the SPF, DKIM and DMARC records for mydomain.com.”
check_email_authentication - “Is mydomain.com on any blacklists?”
check_blacklist
Copy
- “Check this cold email for spam words: (paste the draft)”
analyze_cold_email - “How will this subject line and opening cut off in Gmail on a phone?”
preview_inbox
Lists
- “Clean this lead list and remove duplicates and role addresses: (paste the CSV)”
clean_csv - “Which of these domains are on Google and which on Microsoft?”
segment_esp - “Convert this CSV to Smartlead’s import format.”
convert_csv
Diagnosis
- “Why did this email land in Outlook junk? (paste the headers)”
analyze_microsoft_headers - “What does this bounce mean, and should I keep sending? (paste it)”
analyze_bounces
Planning
- “How many inboxes and domains do I need to send 1,000 cold emails a day?”
plan_infrastructure - “Plan a rotation for 60 inboxes sending 600 a day.”
plan_rotation
Research
- “Does a SURBL listing actually hurt cold email replies?”
find_resources, read_resource - “Which top-level domain should I buy for cold email?”
find_resources, read_resource
What it will not do
- Every tool is read-only. It does not send email, buy inboxes or change your 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.
- Authentication checks cannot guarantee inbox placement, and there are no invented reputation scores: mailbox providers keep those private.
- A free daily limit applies, counted in distinct domains. Checking a domain again the same day does not count again.
- Pasted copy, headers and CSVs are processed to answer and not stored.
When the answer is more inboxes
Ask ChatGPT how many inboxes a send volume needs and it works out the count, the domains and the monthly cost from our prices. The first order is placed in the WarmInboxes app; prewarmed Google, Microsoft 365 and Azure inboxes arrive set up and ready to connect to your sequencer. See the inboxes.
Questions
Is the WarmInboxes ChatGPT plugin 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 for ChatGPT yet?
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.
What does it see, and is anything stored?
It sees what you ask it to check: a domain, an address, or text you paste such as headers, a draft or a CSV. Domains are looked up live. Pasted text is processed to answer and not stored. The privacy policy has the detail.
Can it buy inboxes or change my DNS?
No. Every tool is read-only. When the answer is more inboxes, it works out what to order and what it costs; the first order is placed in the WarmInboxes app, and existing customers can connect the separate purchasing server.
Does it work outside ChatGPT?
Yes. It is a standard remote MCP server at https://warminboxes.com/mcp, so Claude, ChatGPT, Grok, Claude Code, Cursor, VS Code and other MCP clients can all use it.