Mail Certificate

Operating Systems: Windows 10
Program:           Outlook, Thunderbird
published:         - 24.03.2021, Marc Petitmermet (mp)
                   - 14.04.2021, added Thunderbird on Windows information, mp
                   - 28.04.2021, added Thunderbird on macOS information, mp

Introduction

Please follow the official documentation for the Mail certificate:

https://unlimited.ethz.ch/display/itkb/Mail+certificate

Generally, there are three steps:

1. Ordering the certificate
2. Installation of the certificate
3. Configuration of the mail program

Deviations from the above standard procedures are described below.

Thunderbird on Windows

For Thunderbird on Windows follow these steps:

1. Order the certificate
2. Install the certificate using the Windows procedure
   
3. For the configuration of Thunderbird on Windows just follow the instructions for Linux. Please note that the menu item "Preferences" on Linux is called "Options" on Windows.

Thunderbird on macOS

For Thunderbird on macOS follow these steps:

1. Order the certificate
2. Switch to "Android/Linux" as operating system when downloading the certificate to get a certificate format recognized by Thunderbird
3. For the configuration of Thunderbird on macOS follow the procedure for Thunderbird on Linux

Outlook: Invalid Certificate error

Follow the procedure below if you receive the message below when trying to send a message:

"Invalid Certificate: Microsoft Outlook cannot sign or encrypt this message because there are no certificates which can be used to send from the email address 'email address'. Either get a new digital ID to use with this account, or use the Accounts button to send the message using an account that you have certificates for."

1. On the warning windows click on "Change Security Settings..."
   
2. In the Security Properties window click on "Change Settings..."
   
   
3. In the Change Security Settings window select "Choose..."
   
   
4. In the Certificate Details window click on "Install Certificate..." and click through the Certificate Import Wizard.
   
   
   
   
   
   
5. Click on all the OK buttons to close all open windows.
6. Now, sending signed message should work.