A new feature of macOS Mojave is that Plug-ins in Apple Mail have to be activated manually.
To activate the Daylite-Mail-Assistant (DMA) plug-in, please follow these steps:
- Start Apple Mail
- Open the Apple Mail settings in the menu under Mail
- Click the Manage Plug-Ins... button in the tab General
- Check the box next to DayliteMailAssistant.mailbundle
- Click on Apply and Restart Mail
- The sidebar from Daylite Mail Assistant (DMA) should be visible after a restart of Apple Mail