The MAPI connector allows you to specify Server-side Rules, including the Rules that can store incoming messages in an encrypted form.
You may also want to improve security for certain messages received and stored on the Server in clear-text.
Right-click on the selected message in Outlook. A pop-up menu will open:
When you select the Encrypt Message item, the MAPI Connector will send your default Certificate (containing your Public Key) to the Server. The Server will use that Certificate to encrypt the selected message. It will be stored on the Server in the encrypted S/MIME format - as if the message sender has sent it encrypted.
If you want to read Encrypted messages using your MAPI clients (Outlook) and the WebUser Interface, make sure that your Windows desktop system and the WebUser Interface have the same Private Keys and Certificates installed. You can either generate a key and Certificate in the WebUser Interface and then export them to your Windows desktop system, or you can export your keys from the Windows desktop system and import them into your WebUser Interface settings.