Microsoft Agent 365 email signature

An Agent 365 agent with its own Microsoft 365 mailbox sends email as itself. Signatoro gives it a signature in your company brand, with its name, its role and a line saying it is an AI.

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When an Agent 365 agent has its own mailbox

Microsoft Agent 365 lets an organization observe, govern and secure its agents. It is generally available for the Commercial segment, per user, since May 1, 2026.

An agent can also get a Microsoft 365 user account of its own. Microsoft says that with it and the appropriate licenses, "an agent can have a mailbox and OneDrive storage" and be reached through Teams, Outlook, Word comments and email. These accounts are available to tenants in the Frontier preview program.

In this Agentic-User mode the agent acts as its own account, so its email goes out from its own address, under its own name. Microsoft's Mail MCP tools, in preview, create, send and reply to email as the signed-in account, with a Text or HTML body. The Mail tools page lists no signature option, so the signature goes into the body the agent sends, or Exchange adds it in transport.

A signature that signs as the agent

Set the agent up on Signatoro as a company agent. A company owner adds it under "AI agents" in the company's menu, with its name, a role line such as "Support agent" and the agent's mailbox as its email address. It signs with the company brand and details, and a person's phone, photo and links stay off.

Each AI assistant or agent gets its own key or MCP connection and signs as the person it works for or as itself, by default with a line saying it is an AI and whom it acts for. Free includes 1 AI assistant; each person on a Company plan gets 3 AI assistants, and the company gets 3, 10 or 25 agents by size, on top of the people the plan covers.

Company agents come with a paid plan. An owner can also require one disclosure line for every company agent.

AI assistants and company agents Do you have to disclose that an email was written by AI?

Route one: the agent fetches its signature

The agent's code calls the Signatoro API before each send and appends what it returns, so a change to the company brand reaches the agent's next email.

On the company's AI agents page, click "Generate key for" and the agent's name. The key is shown once, and every call with it returns that agent's signature.
Keep the key in the agent's secrets, out of its prompts and logs.
Before each send or reply, call `GET https://signatoro.com/api/v1/signature` with the header `Authorization: Bearer` and the key. Append `html` after an HTML body and `text` after a Text body, as returned.
Tell the agent in its instructions to add no sign-off or signature block of its own.

The Signatoro API for AI agents Add an Outlook signature with Microsoft Graph

Route two: an Exchange mail flow rule

Exchange Online adds HTML or plain text, a signature included, to the top or bottom of messages with a mail flow rule (also known as a transport rule). An Exchange admin sets it up once, and the agent sends its email as it is.

Fetch the agent's signature once with its key and copy the `html` value.
In the Exchange admin center, go to Mail flow, then Rules, then "Add a rule" and "Apply disclaimers".
Under "Apply this rule if", choose "The sender is" and pick the agent's mailbox.
Choose "append a disclaimer" and paste the HTML. Disclaimer text takes HTML tags, inline CSS and images.
Under "Except if", add text from the disclosure line, so a long conversation carries the signature once.
Pick the fallback action for a message the rule is unable to change, such as an encrypted one: Wrap (the default), Ignore or Reject.
Start in "Test without Policy Tips", then set the rule to Enforce.

Mail flow rules for app-sent email

Check one email

The rule holds the copy you pasted, so paste the new HTML after a brand change; the API route picks the change up on the next send. Use one route per agent, so the signature appears once.

Then have the agent send one email to an address outside the company, and read it in that inbox: the agent's name, its role line, the company brand and the disclosure line sit at the bottom.

Microsoft Agent 365 email signature questions

Can a Microsoft Agent 365 agent have its own mailbox?

Yes, in tenants in the Frontier preview program. An agent can get its own Microsoft 365 user account, and with the appropriate licenses that account can have a mailbox and be reached through Outlook and email.

How do I add an email signature to an Agent 365 agent?

Add the agent on Signatoro as a company agent and generate a key for it. The agent calls https://signatoro.com/api/v1/signature with that key before each send and appends the signature, or an Exchange admin adds the signature with a mail flow rule on the agent's mailbox.

Can Exchange add a signature to email from an AI agent's mailbox?

Yes. A mail flow rule with the condition "The sender is" set to that mailbox can append HTML, with inline CSS and images, to every message it sends.

Is Microsoft Agent 365 generally available?

Agent 365 has been generally available for the Commercial segment, per user, since May 1, 2026. Agents with their own user account and mailbox are available to tenants in the Frontier preview program.

Sources

Checked against Microsoft Learn documentation on October 11, 2026.

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