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Set a company-wide email signature in Microsoft 365

Add one signature or disclaimer to all outgoing Microsoft 365 email with an Exchange transport rule, fill names from the directory, and stop repeats in replies.
The Sendoff team4 min read

Microsoft 365 can add one signature or disclaimer to every outgoing email in your organization. You do it with a mail flow rule, also called a transport rule, in the Exchange admin center. The text is added when a message is sent, so recipients see it, but it does not appear in the compose window.

The setup takes a few minutes. Getting the scope and the replies right takes longer, and most of this guide covers that part.

What the rule can and cannot do

The rule adds the same HTML block to each matching message. It can also fill in fields from each sender’s directory account with tokens such as %%DisplayName%%, %%Title%%, %%Department%%, %%Phone%% and %%MobilePhone%%. A token with no value in someone’s profile may leave a blank line, so update profiles before you launch.

Images go in with an IMG tag. Host them at a public HTTPS address so recipients can load them. Tokens fill in text only, so a different headshot for each person needs another method.

Rules do not remove personal signatures. If people have their own signature in Outlook, they also see the company block, and the message ends up with two signatures. Decide which one to keep before you roll out.

Create the rule

  1. Go to admin.exchange.microsoft.com, then Mail flow, then Rules. The direct address is admin.exchange.microsoft.com/#/transportrules.
  2. Select Add a rule, then Apply disclaimers.
  3. Enter a name, for example “Company signature (outgoing)”.
  4. Under Apply this rule if, choose The recipient, then is external/internal, then Outside the organization. That limits the rule to outgoing mail. To cover every message, choose Apply to all messages instead.
  5. Under Do the following, keep “Apply a disclaimer to the message” and “append a disclaimer” selected. Choose “prepend a disclaimer” only if the text should sit above the message.
  6. Select Enter text, paste your HTML and save. Keep it short, and use a table with inline styles for the layout.
  7. Choose a fallback action. Wrap is the default. It puts the original message inside a new one as an attachment. Ignore sends the message without the disclaimer. Reject returns it to the sender. Microsoft says not to use Wrap for rules that affect incoming mail from outside senders, so use Reject there.
  8. Under Except if, choose The subject or body, then Subject or body matches these text patterns. Add a phrase from your disclaimer and save. This stops the block from being added again to replies.
  9. Select Next. On the rule settings page, pick Test without Policy Tips first. It logs what would happen without adding the text. When the log looks right, edit the rule and set it to Enforce.
  10. Select Next, review the settings and select Finish.

Check it before you roll out

Send yourself a plain text email and an HTML email that match the rule, and check the text. Forward one of those test messages to yourself and confirm the disclaimer is not added twice. Send a message that should not match, and confirm it has no disclaimer.

Why the disclaimer repeats on replies

The exception in step 8 is the fix, and it only works if the phrase really appears in the disclaimer. In a 2020 Microsoft Q&A thread, an admin’s first exception had no effect until the exception text was corrected. After you edit the disclaimer, update the exception to match.

Encrypted messages

Some messages cannot be changed, such as encrypted ones. For those, the fallback action decides what happens. If people report missing disclaimers on encrypted mail, check the fallback setting first.

When a signature add-on is also installed

Some companies run a signature add-on next to the rule. CodeTwo’s knowledge base says the disclaimer rule can run again after the add-on has processed a message, which doubles the text. Its fixes are to turn off the disclaimer rule and let the add-on insert both the signature and the disclaimer, or to keep the disclaimer rule above the add-on’s rule and add an exception for the header X-CodeTwoProcessed set to true. CodeTwo also notes that “Stop processing more rules” on its own rule only affects the first pass. Follow the vendor’s current article, since the steps depend on the add-on.

How Sendoff handles this

Sendoff’s Outlook add-in, which your admin deploys, inserts each person’s own Sendoff signature when they start a new message. Each person gets their own design and details, and the signature appears in the compose window. A transport rule gives everyone the same text. To see how the add-in is set up, read the Microsoft 365 integration page, or build a signature first.

Google Workspace works differently

Google does not use a rule. It uses a footer. In the Admin console, go to Menu, then Apps, then Google Workspace, then Gmail, then Compliance. Select the organization, find Append footer, and select Configure.

Google’s footer editor does not accept HTML, so a table-based signature cannot be pasted in. Use formatted text. For an image, enter a URL on a public web server, because images stored in Google Drive cannot be used. By default the footer goes only to recipients outside your organization. Tick the option to add it to internal messages too.

Child organizational units inherit the setting. The footer is not added to messages encrypted with Google Workspace client-side encryption, and changes can take up to 24 hours to apply. The footer can hold up to 10,000 characters. For per-person signatures in Gmail, Sendoff writes each person’s signature into their Gmail settings.

Sources

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