Digital IDs, also known as digital certificates, help to validate your identity, and they can be used to sign important documents electronically. They can also be used to help protect messages by adding a unique code to the message called a digital signature. A digitally signed message proves to the recipient that you, not an imposter, signed the contents of the message, and that the contents haven't been altered in transit.
To find services that issue digital IDs for your use, or services that complement Microsoft 365 and use digital IDs, check out the following websites. It's up to you which one you choose, and others are available that are not in this list, but these are some certificate authorities (CAs) that are qualified to issue digital certificates.
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GlobalSign - To learn more about GlobalSign digital signatures, visit the GlobalSign website.
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IdenTrust - To learn more about IdenTrust's TrustID Secure Email Certificates, visit the IdenTrust website.
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DigiCert - To learn more about DigitCert client certificates, visit the DigiCert website.
After you've obtained a digital ID
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Windows: Follow these instructions to Secure messages by using a digital signature in Outlook.
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Mac: Follow these instructions to Send a digitally signed or encrypted message for Mac.
Notes:
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A digital signature isn't the same as a message signature, which is a customizable salutation. A digital signature adds unique code to a message which only comes from the digital ID held by the true sender.
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Your organization may have its own policies and procedures for using digital IDs and certificates. See your network administrator for more information.
More about digital IDs and signatures
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To learn more about digitally signing documents, see Digital signatures and certificates
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If you're just looking to add an "ink signature" to your Word document, see Insert a signature
Note: To use encryption, your account must have a qualifying Microsoft 365 subscription. Compare all Microsoft 365 Plans.
See also
Set up Outlook to use S/MIME encryption
Verify the digital signature on a signed email message
Secure messages with a digital ID in Outlook
Learn about securing and protecting email messages in Outlook
