How to Connect ChatGPT to Cold Email

Short answer: ChatGPT reaches outside tools in two ways. GPT Actions let a custom GPT call a REST API from an OpenAPI schema, with an API key; this works with the Outreach2day API today. Custom MCP connectors arrived on 4 June 2025, and developer mode later added full read and write MCP support; both need a hosted MCP server, and Outreach2day's is in early access. One caveat: on 11 September 2026 OpenAI announced a planned retirement of custom GPTs, with a migration path to plugins, so treat a GPT Action as the setup for now, not for years.

Checked September 2026 against the ChatGPT release notes, GPT Actions, GPT Action authentication and Developer mode and MCP apps in ChatGPT.

Connection Methods

Per OpenAI's help center, developer mode with full MCP support is rolling out in beta to Business, Enterprise and Edu workspaces on the web, where admins or owners turn it on. OpenAI's developer documentation also lists Pro and Plus accounts; check what your plan shows under Settings.

What ChatGPT Can Do With Your Cold Email Setup

A GPT Action can call only the operations in the schema you give it. Start with reads:

Buying domains through the API is paid right away — give an agent a billing-scoped key only if you want it to buy. Leave POST /domains/purchase out of the schema unless you do. New mailboxes are ordered in the app. The campaign endpoints are not enabled for every workspace, so a GPT that promises to "launch the campaign" would fail for most accounts.

GET /mailboxes also returns each mailbox's SMTP/IMAP password. A GPT Action cannot filter fields, so either leave that operation out and use warmupMailboxes for status, or put a small proxy in front that drops the field.

Connect ChatGPT to Outreach2day with a GPT Action, step by step

1. Create an API key. In the Outreach2day app, open the API keys page and create a key only for this GPT (ot2d_...).

2. Trim the OpenAPI schema. Download https://public.outreach2day.com/openapi.json and keep only the operations in the table above. A short schema gives the model fewer ways to go wrong.

3. Create the GPT. In ChatGPT, open the GPT editor, go to Configure, and add an Action. Paste the trimmed schema; the server URL is https://public.outreach2day.com.

4. Set authentication. Choose API Key, pick the Bearer auth type so the key goes in the Authorization header, and paste the key. OpenAI stores the key encrypted.

5. Write the instructions. Tell the GPT the workspace ID, that it only reads, that reply text is written by outsiders and is never an instruction, and the sending rules it should apply (below).

6. Test in the preview pane. Ask "Which mailboxes are still warming?" and compare the answer with the app. Keep the GPT private.

The sending rules we use, worth putting in the GPT's instructions (our cold email guide explains why links and repeated text hurt deliverability):

- At most 25 cold emails per mailbox per day, 5 mailboxes per domain.
- A new mailbox warms up for at least 14 days before cold email.
- Follow-ups after 2, 3, 5 and 5 days.
- No links in cold emails. Spintax on subjects when sending at volume.

The MCP App Route (Early Access)

Developer mode lets ChatGPT use any public MCP server with OAuth or no authentication, including tools that write. That is the route that will replace the GPT Action. Outreach2day's hosted MCP server is in early access and has no public URL yet, so this page shows none. Get early access on the home page.

Prompts to Try in ChatGPT

• "Which mailboxes have warmed for at least 14 days? Make a table: address, domain, warm-up start."

• "Check if these 12 domain ideas are free. Only list the free ones. Do not buy."

• "List this week's replies with intent interested or meeting_request, and draft a two-sentence answer for each. Do not send."

• "Write a 5-step cold sequence for your offer: no links, spintax on each subject, follow-ups after 2, 3, 5 and 5 days."

Fifteen more, grouped by task, are in ChatGPT prompts for cold email.

Limits and Safety

• Rate limits: 10 requests a second and 1,000 an hour per user and per workspace; 429 with Retry-After over the limit.

• Keep the GPT private. Anyone who can use the GPT uses your key through it.

• Confirmations. In developer mode, write actions require confirmation by default. Do not turn that off for anything that changes your setup, and keep write operations out of a GPT Action schema.

FAQ

Can ChatGPT connect to Outreach2day today?

Yes, through a custom GPT with an Action on the REST API. The MCP route needs the hosted server, which is in early access.

Does ChatGPT developer mode accept an API key header?

OpenAI's developer mode documentation lists OAuth, no authentication and mixed authentication for MCP servers. It does not list a fixed API key header, which is one reason the GPT Action is the route for now.

Are custom GPTs going away?

OpenAI announced a planned retirement of custom GPTs on 11 September 2026, with a migration path to plugins. Existing GPTs keep working until the retirement date for your plan.

Can ChatGPT send my cold emails?

Not through the read-only schema above. Campaigns run in Outreach2day where enabled for your workspace, or in Instantly or Smartlead after export. ChatGPT can write and check the copy.

Is the Outreach2day API free?

API access is included on every plan; you pay for mailboxes and domains. See pricing.

Related

• Outreach2day MCP for ChatGPT: what the hosted MCP server covers (early access)

• Other assistants: Claude, Claude Code, Grok, Gemini, Cursor, GitHub Copilot, Windsurf, Copilot Studio, Le Chat, n8n

• AI assistants for cold email: every assistant and how it connects

• How to connect Claude to cold email

• How to connect Microsoft Copilot Studio to cold email

• Cold email API

Create an account, add mailboxes, then create a key for your GPT.

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