How to Digitally Sign Emails in Outlook

We have already seen how to digitally sign a PDF in order to make it “official” and also usable in the case of contracts or other legal situations. However, if you don’t have to sign a document but a email message, you will need to find alternative solutions. If you have an email address Outlook (for example or you need to know that Outlook Online it allows to sign or encrypt emails digitally, individually or by default all outgoing messages. If this is something you need to do, here are the instructions for turning that feature on.

Why Sign an Email?

The reasons why you might want to digitally sign an email, applying an electronic signature that proves the message came from the indicated sender, or encrypting an email, is a topic in itself. Let’s assume that if you’re interested in digitally signing or encrypting an email, you have a good reason to do so and already understand the pros and cons.

If you don’t know much about digital signatures or encryption, you probably don’t need to worry about either. There’s no point in signing or encrypting your messages if you don’t have to, and in the case of encryption, you’re just doing it so that your recipients aren’t able to read your email.

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But, if email signing and encryption is something you need, here’s how to do it in Outlook Online.

The most important thing to know about signing and encrypting emails in Outlook Online is that it is necessary use the Edge browser and an email account that uses Microsoft Exchange. If you are using Outlook to read your email from Gmail, Yahoo Mail, or any other provider that doesn’t use an Exchange server, this won’t work. Likewise, trying this on Chrome, Firefox, or Safari won’t work.

How to Digitally Sign Emails in Outlook

To get started, open your Microsoft Edge browser and sign in to Outlook Online. Click on “New Message” to open a new email. Click on the three dots in the taskbar to open a drop-down menu and here select the option “Show message options“.

If you just want to encrypt an email, click on “Encrypt” and from here you can also disable forwarding of your email.

In the panel “Message options” that opens, choose whether you want to sign your message, then click the “OK” button.

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The Message options panel, with the Encryption and Digital Signing options highlighted.

If this is the first time you’ve tried to sign or encrypt an email on this computer, you’ll see a message that says “You cannot sign or encrypt this message until you install the S/MIME control. To install S/MIME, click here. ” Click the link to install S/MIME control.

The message stating that the S/MIME control needs to be installed.

You can run the installer directly or download it to your computer and run the installer from there. Assuming you run the installer directly, Edge will ask for confirmation that you want to install the S/MIME control. Click the “Install” button.

The S/MIME Control installation panel.

Once the S/MIME control is installed, Edge will display a message in the bottom right of the window.

The message Edge displays when the S/MIME control has been installed.

Close Edge and then reopen your browser. For reasons known only to Microsoft, Edge may not recognize the S/MIME Control as a Microsoft add-on, so click the three dots found in the top right corner of the interface to open the browser menu and then select “Extensions “.

The 3 dots and browser menu in Edge, with the "Extensions" option highlighted.

Find the extension “Microsoft S/MIME Control” and if it is set to “Off,” click the switch to turn it ON

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The S/MIME Control on/off toggle switch.

Now, log back into Outlook Online and create a new email. Open them again Message options (three dots > Show message options) and choose to encrypt or sign your email. If you are using a domain that has not been registered with S/MIME control, you will see a message telling you to add the domain. Click the link to open the S/MIME control options.

The "add domain" error message.

In the panel “S/MIME control options“, check the box next to “Allow work or school domains“, add your email domain in the text box, then click the “ buttonSave“.

The "S/MIME Control options" panel.

Now you will have to restart Edge again and log in to Outlook Online again. You will finally be able to send signed and encrypted emails.

If you want to sign or encrypt every email you send by default, click Settings > View all Outlook settings.

Outlook's "View all Outlook settings" option.

Click Email > S/MIME.

Outlook's Settings menu, with the "S/MIME" option highlighted.

Enable one or both of the encryption and signing options, then click the “Save“.

The S/MIME settings.

All emails you send will now be automatically encrypted and/or signed, depending on the options you have chosen.

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