Step 1: import the Certificate
- After you receive the certificate from the CA, follow their instructions to download it to your computer. This usually comes as a .p12 file.
- double-click the certificate file and follow the wizard to import it.
Step 2: install the Certificate in Windows
- Open Windows Certificate Manager;
- press Windows + R;
- type certmgr.msc
- press Enter. This will open the Certificate manager;
- navigate to Personal > Certificates;
- right-click on the empty space, select All Tasks > Import;
- use the wizard to browse to the location of your .p12 Certificate file;
- you will need to enter the password provided when you received the Certificate.
Once imported, the certificate should appear under Personal > Certificates with your name or email address.
Step 3: configure S/MIME in Microsoft Outlook
- Open Outlook: launch Microsoft Outlook on your desktop;
- go to Trust Center Settings. Click on File in the top-left corner;
- select Options from the left-hand menu;
- in the Options window, go to Trust Center and click Trust Center Settings;
- in the Trust Center window, select Email Security;
- under the Encrypted Email section, click Settings;
- in the Settings window, under Certificates and algorithms, select the Choose button next to Signing Certificate;
- select the S/MIME Certificate from the list (the one you just imported);
- make sure the same Certificate is selected under Encryption Certificate;
- choose encryption and hashing algorithms if required (typically RSA for signing, AES for encryption).
Enable digital signatures and encryption (optional):
- if you want to always sign your emails, check the box that says Add digital signature to outgoing messages;
- for encrypting emails by default, check Encrypt contents and attachments for outgoing messages;
- click Ok to save your changes and close the dialog boxes.
The recipient needs an S/MIME certificate and the correct configuration in their email client to open encrypted messages.
This guide should help you configure S/MIME certificates in Microsoft Outlook. If you're using Outlook for Office 365, the steps are very similar, but the user interface may vary slightly depending on the version.
Step 4: test the S/MIME Configuration
- Create a new email. In the Options tab of the message, click the Sign icon (it looks like a pen);
- compose and send the email.
Send an encrypted email (optional):
- to send an encrypted email, you must have the recipient’s public key (which they usually send to you in a signed email). Open a new email, go to the Options tab, and click Encrypt;
- compose and send the encrypted message.
Public Keys are shared through digitally signed emails. When someone receives a signed email, they automatically receive your public key.
Make sure both sender and recipient use email clients that support S/MIME (Outlook, Apple Mail, etc.).