Recipient Guard

Recipient Guard checks who you're actually emailing — before the message leaves.

AutoComplete is the single most common cause of misdirected email. You type "Dave", Outlook offers a Dave, and it's the wrong one. Recipient Guard pauses that send and shows you exactly who the message is going to.

What it catches

• The wrong pick from AutoComplete — you're emailing an address you don't normally use for that person, even when it's the only recipient on the message.
• Look-alike recipients — two people sharing a display name, or the same username on different domains (john.doe@acme.com vs john.doe@acme-invoices.com).
• External recipients — anyone outside your organisation.

How it works

When you hit Send, Recipient Guard reviews the recipients and — only if something looks off — pauses and shows you the full list, with the questionable one flagged and the reason why. You can send anyway, open a full review, or go back and fix it. Nothing to configure; it works from the moment it's installed.

Important — how Recipient Guard is installed

The send-time check uses Outlook's event-based activation. Microsoft enables that feature only when an add-in is deployed by a Microsoft 365 administrator, so what you get depends on how it's installed:

• Deployed by an administrator (Microsoft 365 admin center → Settings → Integrated apps) — the complete product. Recipients are checked automatically every time someone selects Send.
• Installed by an individual from this listing — the Recipient Guard pane is available to check the recipients of a message on demand, but the automatic send-time check does not run.

If you administer your own Microsoft 365 tenant, you can deploy Recipient Guard to yourself in a few minutes — see our support page for step-by-step instructions.

Built for the way you actually send

• Review before sending — see every recipient, with the risky one highlighted.
• Delay 1 minute & send — a cooling-off window with a cancel button, for when you want a second look.
• Don't warn about this address — trust an address, or a whole trusted domain (public webmail domains like gmail.com are deliberately excluded), and it stops asking. Manage and remove trusted entries any time from the pane.
• Smart detection — optionally learns who you usually email (from your Microsoft 365 frequent contacts, and from your saved Outlook contacts if you allow it) so it can spot a single wrong recipient. One click to enable.

Works everywhere you use Outlook — Outlook on the web, new Outlook, classic Outlook on Windows, and Outlook on Mac. No account or licence key required.

How Recipient Guard runs in Outlook

Recipient Guard uses Outlook's event-based activation (LaunchEvent) together with the Smart Alerts feature on the OnMessageSend event.

When it runs: only when you select Send on a message you are composing. It does not run on messages you receive, and it does not run in the background at any other time.

What it reads: only the recipient fields of the message being sent (To, Cc and Bcc) and your own mailbox address, which it uses to work out which recipients are outside your organisation. If you turn on the optional Smart detection feature, it also reads your Microsoft 365 frequent-contact list and, where you have granted permission, the contacts saved in your Outlook Contacts folder. The subject, message body and attachments are never read.

Microsoft Graph permissions it asks for: none at all unless you turn on Smart detection, which is off until you do. When you turn it on, Microsoft asks for your consent to People.Read (your frequently-contacted people) and User.Read (sign-in only — no data is read with it). Recipient Guard may additionally ask for Contacts.Read, to read the contacts saved in your Outlook Contacts folder: Microsoft builds the frequently-contacted list from mail you have already sent, so it cannot include someone you have saved but not yet written to — which is exactly when a wrong address is easiest to pick. Contacts.Read is requested in addition to the other two, never instead of them. If it is not granted, Smart detection carries on working from your frequently-contacted people alone. Your consent can be reviewed or withdrawn at any time at myapps.microsoft.com.

What it inserts or changes: nothing. Recipient Guard does not insert, add, modify or remove any content in your message — no text, no headers, no attachments and no recipients. Its only effect is to pause the send and show you a dialog.

What you see, and when: the dialog appears only if a recipient matches one of the checks above. If nothing looks wrong, the message sends normally with no dialog and no delay.

You always stay in control: the alert runs in PromptUser mode, so you can select Send anyway and the message goes exactly as you wrote it. You can also select Don't send to return to the message, or Review and trust to open the full review.

Privacy by design — there is no Recipient Guard server. All recipient analysis runs locally inside Outlook. The only data it stores — your contact list and your whitelist — stays inside your own Microsoft 365 mailbox using Office roaming settings. No recipient data, contact data, or message content is ever sent to us or any third party. Message bodies and attachments are never read.

Free to install and use.