How to add your email signature to emails Claude sends

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

How Claude sends email

Claude can draft and send email, and whether your signature appears depends on the route. With the Gmail connector, Claude searches, drafts, sends, replies and forwards in Gmail, and by default asks for your approval before each send, reply or forward. With the Microsoft 365 connector, Claude drafts and sends Outlook email from a work account once an admin enables write tools. Personal Outlook.com accounts cannot connect.

Email Claude sends through the Gmail connector is built by the connector outside Gmail's compose window. 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. A connector email therefore carries no signature unless Claude writes one into the body. The Gmail connector's draft and send tools take a plain-text body and an HTML body.

The Microsoft 365 connector sends Outlook email from Claude's side, outside Outlook's compose window, where Outlook adds the signatures set in its Signatures settings. Check one email the connector sent in your Outlook Sent folder: if it ends without your signature, Claude has to write the signature in, the same as with the Gmail connector.

Three Claude routes leave the signature to your mail app. Claude for Outlook drafts replies unsent in Outlook's compose pane, and Anthropic says it leaves the closing off so Outlook can append your configured signature. Claude on iPhone and Android composes emails that open in your mail app with the text filled in, and you send them from there. Claude in Chrome clicks and types in your real Gmail tab, like a person would.

Claude Code signed in with a claude.ai account can use the connectors you added in claude.ai, plus any MCP server or script you give it. With the Claude API or the Agent SDK, your own code or tool sends the email, so it adds the signature. Signatoro has found that the Gmail tool built into chat assistants drops every image from the HTML it is given, so a signature sent through it arrives without its picture.

Add your signature to emails Claude sends

Claude for Outlook and Claude on your phone

1. Set your signature in Outlook or your phone's mail app with the Outlook guide or the guide index, turned on for new messages and for replies and forwards.
2. Ask Claude to draft the email.
3. Open the draft in Outlook's compose pane or your mail app and check it ends with your signature, once.
4. If it is missing in new Outlook, select "Signature" in the "Insert" group on the "Message" tab and choose your signature.
5. Send the email yourself.

Claude in Chrome

1. Set your signature in Gmail with the Gmail guide, chosen as the default for new emails and for replies.
2. In your request, tell Claude not to type a signature, because Gmail adds it.
3. Before Claude sends, check the compose window shows your signature once.

The Gmail and Microsoft 365 connectors

1. On Signatoro, click "Copy as text".
2. In Claude, click your initials in the lower left corner, then "Settings".
3. Under "Instructions for Claude", write "End every email you draft or send with this signature, exactly as written:" and paste the text below it.
4. Ask Claude to draft an email and check that it ends with those lines.

If you open Claude's Gmail draft and send it from Gmail yourself, you can use Gmail's own signature instead: in the compose window, click "Insert signature" at the bottom and pick yours. In that case, leave the signature out of Claude's instructions so the email does not end with two.

Claude Code, the Claude API and the Agent SDK

1. Save your signature on the signature page.
2. Under "For tools and assistants", click "Generate API key". Store the key as an environment variable or secret, and keep it out of prompts, chats and CLAUDE.md.
3. Have your script or tool call GET https://signatoro.com/api/v1/signature with Authorization: Bearer <key> before each send.
4. Append html after the HTML body and text after the plain-text body, then send through the Gmail API 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.

Claude email signature questions

Why doesn't Claude add my Gmail signature when it sends an email?

Claude's Gmail connector sends exactly the body Claude writes, and Gmail adds a saved signature only to new emails composed in the Gmail web interface, according to Google's Gmail API reference. An email Claude sends, replies or forwards through the connector therefore goes out without the signature from Gmail Settings. Give Claude the signature text in "Instructions for Claude" so it ends every email with it.

Why is the logo missing from my signature in a Gmail draft Claude made?

Signatoro has found that the Gmail tool built into chat assistants such as Claude drops every image from the HTML body it is given, including linked images and inline attachments, while keeping the text. A signature logo in a Claude Gmail draft therefore disappears. For those drafts, use the text version of the signature, or open the draft in Gmail and click "Insert signature" at the bottom of the compose window to add your Gmail signature, logo included.

How do I get Claude to put my signature at the bottom of emails it writes?

Claude applies "Instructions for Claude", found under "Settings", to all of your conversations. Paste your signature there as plain lines with an instruction such as "End every email you draft or send with this signature, exactly as written." For email work kept in one Claude project, project instructions do the same for that project only. Signatoro's "Copy as text" button copies a signature as plain lines ready to paste.

Why did Claude put a phone number I don't recognize in my email signature?

When Claude writes a sign-off without your real details, it can fill the gaps with invented ones, such as a phone number, and present them as yours. Claude's Gmail connector has no tool that reads the signature saved in Gmail Settings. Give Claude your exact signature in "Instructions for Claude" and ask it to copy it unchanged, and check every draft's signature before it goes out.

Does Claude for Outlook add my Outlook signature?

Claude for Outlook writes each reply as an unsent draft in Outlook's compose pane, and Anthropic says Claude leaves the closing off so Outlook can append the signature you configured. The signature comes from Outlook's own Signatures settings, so set it there for replies and forwards. If a draft arrives without it, add it from "Signature" in Outlook's "Insert" group before you send.

For agents

• First work out your route. In the person's own mail app or browser tab (Claude for Outlook, Claude in Chrome, a phone compose sheet), the mail app adds the signature: write no closing block and never paste a second signature.
• Through the Gmail or Microsoft 365 connector, nothing adds a signature. End the body with the text signature from the person's 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 Anthropic's, Google's and Microsoft's own documentation on 2026-09-25:

• Use Google Workspace connectors
• Connect to Microsoft 365
• Use Claude for Outlook
• Get started with Claude in Chrome
• Use Claude with iOS apps
• Use Claude with Android apps
• Understanding Claude's personalization features
• Connect Claude Code to tools via MCP
• Give Claude custom tools (Agent SDK)
• REST Resource: users.settings.sendAs (Gmail API)
• Create a Gmail signature
• How to add and change an email signature in Outlook