Initial situation: When trying to send an encrypted email from Outlook, the following error message appears: Checksum mismatch at 0 of 20.

Solution: The following steps are necessary as a workaround until an updated version of the add-in fixes this error:

1. Delete the REDDCRYPT accounts in the REDDCRYPT Addin settings
2. Close Outlook
3. Delete the accounts.json file, which you can find under %appdata% for Windows\Common
4. Start Outlook and add the existing account in the REDDCRYPT Addin again