How to add your email signature to emails ChatGPT sends

Get your email signature on emails ChatGPT writes or sends through Gmail or Outlook: custom instructions, pasting into your mail app, and the OpenAI API.

Published September 25, 2026

If you already have a signature, check "How ChatGPT sends email" for the route ChatGPT takes to your mail: the route decides whether your mail app adds the signature or ChatGPT has to. If you need one, make it free on Signatoro, then click "Copy signature" for your mail app or "Copy as text" for ChatGPT's custom instructions.

How ChatGPT sends email

ChatGPT can draft and send email from a conversation when Gmail or Outlook is connected. OpenAI's release notes say ChatGPT creates a draft and you can choose to send it without leaving ChatGPT, on the web, for Plus, Pro, Business and Enterprise plans. OpenAI treats sending an email as an important action, so by default ChatGPT asks you before it sends.

An email ChatGPT sends from the chat is written in ChatGPT, outside Gmail's and Outlook's compose windows. Google's Gmail API reference says a Gmail signature is included in messages composed in the Gmail web interface and is added to new emails only, and Outlook adds its signatures in its own compose window. Check one email ChatGPT sent in your Sent folder: if it ends without your signature, ChatGPT has to write the signature in.

OpenAI documents the Outlook Email app sending plain-text email from shared or delegated mailboxes. OpenAI does not say whether other emails ChatGPT sends keep images. Signatoro has found that the Gmail tool built into chat assistants drops every image from the HTML it is given, so the reliable signature for mail ChatGPT sends is the text one: name, role and links.

The route where your mail app adds the signature is the one you finish yourself: you copy ChatGPT's text into a new email in Gmail or Outlook and send it. Agent mode in OpenAI's ChatGPT Atlas browser works in your current browsing session, so in a signed-in Gmail or Outlook tab the mail app adds its signature there too. OpenAI says the older ChatGPT agent is no longer available. With the OpenAI API, your own code sends the email and adds the signature.

Add your signature to emails ChatGPT sends

Emails ChatGPT sends from a chat

On Signatoro, click "Copy as text".
In ChatGPT on the web, open "Settings" and select "Personalization". In the iPhone or Android app, select "Customize ChatGPT" in "Settings".
Make sure "Enable customization" is on.
In the "Custom Instructions" field, write "End every email you draft or send with this signature, exactly as written:" and paste the text below it.
Ask ChatGPT to draft an email and check that it ends with those lines before you approve the send.

Emails you copy from ChatGPT into Gmail or Outlook

Set your signature in your mail app with the Gmail guide or the Outlook guide, turned on for new emails and replies.
Ask ChatGPT for the email text without a signature.
Start a new email or reply in Gmail or Outlook: the signature appears on its own.
Paste ChatGPT's text above the signature and send.

The OpenAI API and your own automations

Save your signature on the signature page.
Under "For tools and assistants", click "Generate API key". Store the key in your platform's secret store, and keep it out of prompts, chats and system messages.
Before each send, have your code call GET https://signatoro.com/api/v1/signature with Authorization: Bearer <key>.
Append html after the HTML body and text after the plain-text body, then send through the Gmail API, Microsoft Graph or your mail library.

Signatoro's signature API guide has the full request, the responses and a Gmail API example. Each call returns the current version of the signature; free accounts have a monthly request limit, and people in a company on a plan have none.

For agents

First work out your route. If the person finishes the email in Gmail or Outlook, or you work in their own signed-in mail tab, the mail app adds the signature: write no closing block and never paste a second signature.
If you send through the Gmail or Outlook connection, nothing adds a signature. End the body with the text signature from the person's custom instructions, exactly as given; if there is none, ask the person for it.
Through your own code, fetch GET https://signatoro.com/api/v1/signature per send and append html or text, as the signature API guide describes.
Never ask for, repeat or store a Signatoro API key in a conversation.

Sources

Checked against OpenAI's, Google's and Microsoft's own documentation on 2026-09-25:

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How ChatGPT sends email

Add your signature to emails ChatGPT sends

Emails ChatGPT sends from a chat

On Signatoro, click "Copy as text".

In ChatGPT on the web, open "Settings" and select "Personalization". In the iPhone or Android app, select "Customize ChatGPT" in "Settings".

Make sure "Enable customization" is on.

In the "Custom Instructions" field, write "End every email you draft or send with this signature, exactly as written:" and paste the text below it.

Ask ChatGPT to draft an email and check that it ends with those lines before you approve the send.

Emails you copy from ChatGPT into Gmail or Outlook

Set your signature in your mail app with the Gmail guide or the Outlook guide, turned on for new emails and replies.

Ask ChatGPT for the email text without a signature.

Start a new email or reply in Gmail or Outlook: the signature appears on its own.

Paste ChatGPT's text above the signature and send.

The OpenAI API and your own automations

Save your signature on the signature page.

Under "For tools and assistants", click "Generate API key". Store the key in your platform's secret store, and keep it out of prompts, chats and system messages.

Before each send, have your code call GET https://signatoro.com/api/v1/signature with Authorization: Bearer <key>.

Append html after the HTML body and text after the plain-text body, then send through the Gmail API, Microsoft Graph or your mail library.

For agents

First work out your route. If the person finishes the email in Gmail or Outlook, or you work in their own signed-in mail tab, the mail app adds the signature: write no closing block and never paste a second signature.

If you send through the Gmail or Outlook connection, nothing adds a signature. End the body with the text signature from the person's custom instructions, exactly as given; if there is none, ask the person for it.

Through your own code, fetch GET https://signatoro.com/api/v1/signature per send and append html or text, as the signature API guide describes.

Never ask for, repeat or store a Signatoro API key in a conversation.