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Obtaining a SMIME Certificate to Sign or Encrypt Emails

Free Certificates from Comodo

Comodo has perhaps one of the easiest procedures for requesting an email certificate. They are free, good for a year, can be picked up using most browsers, and can be either 512, 1024 or 2048 bits long. 

Fill out the Application for Secure Email Certificate and you will be emailed the instructions to download a CollectCCC.p7s file to your computer. 

Getting the Key Ready on the Mac

  • Double-click the downloaded CollectCCC.p7s file and Keychain Access will ask you to import it. The default keychain is Login, and this is OK. Click the Add button.
  • In Keychain Access, click on login and then Certificates below.
  • On the right you should see:

1) a certificate titled: "COMODO SHA-256 Client Authentication and Secure Email CA" and

2) a personal certificate with your email address (expandable by clicking on a triangle to the left in order to see the email address).

  • In Keychain select "COMODO SHA-256 Client Authentication and Secure Email CA" and from the File menu select Export Items... from the File menu. The file format should be Certificate (.cer).
  • Save the file to the Desktop.
  • In Keychain, expand the personal certificate with your email address using the triangle so that underneath you see it's key.
  • Select the certificate (not the key) and select Export Items... from the File menu. The file format should be Personal Information Exchange (.p12).
  • Save the file to the Desktop.
  • Enter a password to protect the key.

 

Importing the Certificate into Postbox

To import a certificate into Postbox:

  • Postbox > Preferences (Mac) or Options (Windows) > Advanced > Certificates > View Certificates > Your Certificates > Import...
  • Select the .p12 file for import. You will be prompted for the password you used when you exported (or backed up) the file.
  • Next go to: Postbox > Preferences (Mac) or Options (Windows) > Advanced > Certificates > View Certificates > Authorities > Import... 
  • Select the .cer file for import. In the pop-up dialog please select all of the checkboxes and click OK.

 

Setting up an Identity to Sign or Encrypt

Once you have imported your certificate into Postbox, it will be available for pairing with one or more accounts in Postbox.

  • Go to Postbox > Preferences (Mac) or Options (Windows) > Accounts > <your account> > Security
  • Click the Select button under Digital Signing and/or Encryption. You'll be given an option to also use this certificate when people send you encrypted messages, and we recommend that you select OK.

 

Sending a Signed Message

Compose a message, and from the Options menu select Security > Digitally Sign This Message.

 

 

This article includes content contributed by the MozillaZine Knowledge Base. Thank you to all of the contributors who created this content and to MozillaZine for sharing this information.