# Organisation-Wide Email Signatures in Microsoft 365: Options

> Compare ways to apply one email signature to all staff in Microsoft 365: mail flow rule disclaimers, per-mailbox Outlook on the web settings and add-ins.

Source: https://www.epifive.com/blog/organisation-wide-email-signatures-microsoft-365 · Published 2026-10-26 · EpiFive

## Key takeaways

- A Microsoft 365 mail flow rule using Apply disclaimers can append or prepend an HTML signature to messages for the whole organisation from one place.
- The disclaimer text supports sender tokens such as %%DisplayName%% and %%Title%%, which pull values from each user's directory properties.
- Add an exception that matches unique text from the signature so it is not added again on every reply in a conversation.
- Set-MailboxMessageConfiguration signature settings apply to Outlook on the web and the new Outlook only, not to classic Outlook.
- Test the rule in test mode first and pick a fallback action deliberately, because the default Wrap action creates a new message with the original attached.

The simplest way to give every Microsoft 365 user the same signature is a mail flow rule that uses the **Apply disclaimers** action in the Exchange admin center. It adds your HTML signature to the bottom or top of messages as they pass through Exchange Online and can pull each sender's name, title and phone number from their directory properties. The trade-off is that the signature is added in transit, so it is not placed under the user's reply text and users do not see it while composing.

## Who this is for and what you will have

This guide is for administrators of small and mid-sized Microsoft 365 tenants who want consistent signatures without manual setup on every device. By the end you will understand the options, have a working mail flow rule with sender tokens, know how to avoid duplicate signatures in threads, and know the alternatives when a rule is not enough.

## The options at a glance

| Option | Where it runs | Placement | Controlled by | Main limitation |
| --- | --- | --- | --- | --- |
| Mail flow rule (Apply disclaimers) | Exchange Online, in transit | Bottom (append) or top (prepend) of the message | Admin, centrally | Not shown while composing or in the sender's Sent Items; sits at the end of the whole message |
| Per-mailbox settings with PowerShell | Outlook on the web and new Outlook | Normal signature position | Admin, per mailbox | Needs roaming signatures disabled; not used by classic Outlook |
| User-created signatures | Outlook client or web | Normal signature position | Each user | Not consistent |
| Third-party signature service or add-in | Varies by product | Varies | Admin | Extra cost and a separate service to evaluate |

Microsoft's documentation describes the mail flow rule approach and notes that users can apply signatures to their own outgoing messages in Outlook or Outlook on the web. The per-mailbox settings come from the PowerShell references. The placement and Sent Items behaviour in the table follows from the rule running in transit, after the sender's client has finished with the message; it is a consequence of how the rule works rather than a documented limit. Third-party products are described only in general terms because their features differ.

## Prerequisites

- A role that can manage mail flow rules (the "Mail flow" entry in the Exchange Online feature permissions).
- Exchange Online PowerShell if you want to script the rule. Connect with `Connect-ExchangeOnline`. If that fails, see [/blog/connect-exchangeonline-errors-fix](https://www.epifive.com/blog/connect-exchangeonline-errors-fix).
- Complete directory data. Sender tokens such as `%%Title%%` and `%%Phone%%` read values from each user's properties, so check them in the Microsoft 365 admin center before you roll out. A missing value produces a gap in the signature.
- A signature design in HTML, ideally simple. Disclaimer text can include HTML tags and inline CSS, and images can be added with the IMG tag, but email clients render complicated markup differently.

## Create the mail flow rule in the admin center

1. Open the Exchange admin center at `https://admin.exchange.microsoft.com` and go to **Mail flow** > **Rules**.
2. Select **Add a rule**, then **Apply disclaimers**.
3. On **Set rule conditions**, enter a unique **Name**.
4. Under **Apply this rule if**, choose who gets the signature. To limit it to external mail, select **The recipient** > **is external/internal**, then **Outside the organization**. To apply it to everything that enters or leaves the organisation, choose **Apply to all messages**. By default, mail flow rules apply to incoming and outgoing messages, so add a condition if you only want outgoing mail signed.
5. Under **Do the following**, make sure **Apply a disclaimer to the message** and **append a disclaimer** are selected. Choose **prepend a disclaimer** instead to place the text at the top.
6. Select **Enter text** and paste your HTML signature.
7. Select **Select one** to set the fallback action (explained below).
8. Under **Except if**, add **The subject or body** > **Subject or body matches these text patterns** and enter a phrase that appears only in your signature. This stops the rule adding another copy on each reply.
9. On **Set rule settings**, leave **Rule mode** at **Enforce** or choose **Test without Policy Tips** first.
10. Review and select **Finish**.

### Use sender tokens

The disclaimer text supports tokens that use values from the sender. Microsoft lists, among others, `%%DisplayName%%`, `%%FirstName%%`, `%%LastName%%`, `%%Title%%`, `%%Department%%`, `%%Company%%`, `%%Office%%`, `%%Phone%%`, `%%MobilePhone%%`, `%%StreetAddress%%`, `%%City%%`, `%%PostalCode%%`, `%%UserPrincipalName%%` and `%%WindowsEmailAddress%%`.

A sample signature body:

```text
<p><strong>%%DisplayName%%</strong><br>
%%Title%%, %%Department%%<br>
Contoso Ltd<br>
T: %%Phone%% | M: %%MobilePhone%%<br>
<a href="https://www.contoso.com">www.contoso.com</a></p>
```

If a user has no value for a token, that part of the signature is blank, so a line such as `M: %%MobilePhone%%` may show an empty "M:". Keep optional fields on their own line or leave them out.

### Create the same rule with PowerShell

`New-TransportRule` creates the rule. The Microsoft example adds an HTML disclaimer to messages sent outside the organisation:

```powershell
New-TransportRule -Name "External Disclaimer" -SentToScope NotInOrganization -ApplyHtmlDisclaimerText "<h3>Disclaimer Title</h3><p>This is the disclaimer text.</p><img alt='Contoso logo' src='http://www.contoso.com/images/logo.gif'>"
```

To put the text at the top, add `-ApplyHtmlDisclaimerLocation Prepend`. To set the fallback, use `-ApplyHtmlDisclaimerFallbackAction`. Pointing the image at an address on your own website over HTTPS is safer than the plain HTTP address used in the sample, and gives recipients' mail clients a chance to load it.

A fuller version for outbound mail with the duplicate-prevention exception might look like this. The `-ExceptIfSubjectOrBodyMatchesPatterns` parameter is the PowerShell counterpart of the exception in the admin center. Test the rule on a few messages before enforcing it:

```powershell
New-TransportRule -Name "Company signature" `
  -SentToScope NotInOrganization `
  -ApplyHtmlDisclaimerLocation Append `
  -ApplyHtmlDisclaimerFallbackAction Wrap `
  -ApplyHtmlDisclaimerText "<p><strong>%%DisplayName%%</strong><br>%%Title%%<br>Contoso Ltd</p>" `
  -ExceptIfSubjectOrBodyMatchesPatterns "Contoso Ltd"
```

## Choose the fallback action

If the rule cannot modify a message, for example because it is encrypted, the fallback option decides what happens:

| Fallback | What happens |
| --- | --- |
| Wrap (default) | A new message carries the disclaimer and the original is attached to it |
| Ignore | The original is delivered without the signature |
| Reject | The original is returned to the sender in a non-delivery report |

Microsoft warns not to use **Wrap** in rules that affect incoming messages from external senders, because it interferes with Safe Attachments scanning, and to use **Reject** instead. To find rules that already do this, run:

```powershell
Get-TransportRule | where {$_.ApplyHTMLDisclaimerFallbackAction -eq 'Wrap' -and $_.FromScope -eq 'NotInOrganization'}
```

For an outbound-only signature, **Ignore** is often the least disruptive choice, since a missing signature on an encrypted message is usually acceptable. Decide this deliberately.

Also remember that when **Wrap** is used, later rules examine the new wrapper message rather than the original. Microsoft advises giving other rules a higher priority than the disclaimer rule so they run first.

## Alternative: per-mailbox signatures for Outlook on the web

If you want signatures that appear in the normal position and in Sent Items, you can configure them per mailbox. This applies to Outlook on the web and the new Outlook for Windows only. The Set-MailboxMessageConfiguration reference states that these settings are applied in Outlook on the web and that some also apply to the new Outlook client, and are not used in Outlook (classic), Exchange ActiveSync or other clients.

Roaming signatures in Outlook on the web and the new Outlook must be switched off first. The `PostponeRoamingSignaturesUntilLater` parameter of `Set-OrganizationConfig` controls this, with `$true` disabling roaming signatures. Its reference notes that for Windows clients the registry setting to disable roaming signatures still works, and that when roaming signatures are disabled, admins can use the signature-related parameters on `Set-MailboxMessageConfiguration`, such as `AutoAddSignature`, `AutoAddSignatureOnReply` and `SignatureHtml`. It also says Microsoft has no plans to support roaming signature management in Microsoft Graph.

```powershell
Set-OrganizationConfig -PostponeRoamingSignaturesUntilLater $true

Set-MailboxMessageConfiguration -Identity user@contoso.com `
  -SignatureHtml "<p><strong>Ayla Demir</strong><br>Operations Manager<br>Contoso Ltd</p>" `
  -AutoAddSignature $true `
  -AutoAddSignatureOnReply $true
```

Because this is per mailbox, you would loop over users and build the HTML from their directory properties yourself, and it affects only the web and new Outlook clients. Test with one pilot mailbox first before rolling it out.

## Other approaches

Independent software vendors are encouraged by Microsoft to use the Outlook signature API with event-based add-in hooks, and third-party signature services exist that build on it or on mail flow. Evaluate any of these on their own documentation and pricing: whether they insert the signature under the reply text, support banners and campaigns, and handle mobile clients. This guide does not compare vendors.

## Test the rule

Microsoft's verification steps are:

1. Send yourself both a plain text email and an HTML email that match the conditions and exceptions, and confirm the signature appears as intended.
2. Forward those messages to yourself to verify you do not get a second copy of the signature. Replying to them is a sensible extra check.
3. Send messages that should not match, such as internal messages if the rule is external only, and confirm they are untouched.

It is also worth opening the results in a few mail clients, including a phone, because HTML renders differently between them.

Use `Get-MessageTraceV2` or the message trace feature if a message did not behave as expected. See [/blog/message-trace-exchange-online-get-messagetracev2](https://www.epifive.com/blog/message-trace-exchange-online-get-messagetracev2).

## Troubleshooting

### The signature appears more than once in a thread

The exception is missing or does not match. Add an exception on the subject or body with a distinctive phrase from the signature, such as the company line.

### Users do not see the signature when composing

This is expected with a mail flow rule. The text is added after the message leaves the user's client, so it is not in the compose window or in the saved Sent Items copy. Recipients receive it.

### Tokens show as blank

The user's directory attribute is empty. Fill in the properties for the user, then send a new test message.

### Other rules do not act on messages that carry the signature

If the fallback action is Wrap, the original message may be wrapped as an attachment. Review rule priorities as described above, or choose a different fallback.

### Messages are returned with a non-delivery report

The fallback is set to Reject and the rule could not modify the message, for example an encrypted one. Change the fallback to Ignore if you would rather deliver without the signature.

### Signature settings on a mailbox do not stick

Check that roaming signatures are disabled for the organisation and wait for the setting to apply. Remember that the PowerShell signature settings do not drive classic Outlook.

## Checklist

- Decide between a mail flow rule (central, appended or prepended) and per-mailbox settings (web and new Outlook only).
- Clean up user properties used by the sender tokens.
- Build a simple HTML signature and host any image on your own HTTPS site.
- Add a condition for outbound mail and an exception for duplicates.
- Choose the fallback action deliberately and review existing Wrap rules.
- Run the rule in test mode, then enforce it.
- Send test messages, replies and forwards from several clients.

For more on how rules are evaluated and ordered, see [/blog/exchange-online-mail-flow-rules-guide](https://www.epifive.com/blog/exchange-online-mail-flow-rules-guide).

## References

- Organization-wide message disclaimers, signatures, footers, or headers in Exchange Online: https://learn.microsoft.com/en-us/exchange/security-and-compliance/mail-flow-rules/disclaimers-signatures-footers-or-headers
- Set-OrganizationConfig: https://learn.microsoft.com/en-us/powershell/module/exchangepowershell/set-organizationconfig
- Set-MailboxMessageConfiguration: https://learn.microsoft.com/en-us/powershell/module/exchangepowershell/set-mailboxmessageconfiguration
- New-TransportRule: https://learn.microsoft.com/en-us/powershell/module/exchangepowershell/new-transportrule

## Frequently asked questions

### How do I add the same signature to all emails in Microsoft 365?

Create a mail flow rule in the Exchange admin center under Mail flow and Rules, choose Apply disclaimers, set the condition to all messages or messages to external recipients, and enter the signature as HTML text with sender tokens such as %%DisplayName%%. The rule appends the text to the message as it passes through Exchange Online.

### Can a mail flow rule put the signature above the reply text?

A disclaimer rule can append text at the bottom or prepend it at the top of the message. Microsoft's guidance does not describe a way to insert it directly under the user's new text but above the quoted conversation, so for that behaviour you need Outlook client signatures or an add-in.

### Why does the signature not show in the sender's Sent Items?

A mail flow rule modifies the message in transit, after the sender's client has saved its copy. Users therefore do not see the rule-based signature in the preview they type, and it is not in the saved copy in Sent Items. Recipients do see it.

### Can I push signatures to Outlook with PowerShell?

For Outlook on the web and the new Outlook for Windows you can set SignatureHtml, AutoAddSignature and AutoAddSignatureOnReply per mailbox with Set-MailboxMessageConfiguration, but only once roaming signatures are disabled with Set-OrganizationConfig -PostponeRoamingSignaturesUntilLater. These settings are not used by classic Outlook.