Postbox will turn dates (ex: "next Thursday" and "5/15/2017") inside email messages into links that you can click to add events to your calendar.
On Windows, the default calendar is Google Calendar.
On macOS, the default calendar is Calendar app, and Postbox will add events to the first calendar on your list. Drag and drop the desired calendar to the top of your list, and this can either be your default calendar or another calendar.
If clicking on a detected date does not add the event to Calendar, please check to make sure Postbox has access to the calendar by going to macOS System Preferences > Security & Privacy > Privacy > select Calendar, and then make sure that Postbox is selected.
To use Google Calendar on the Mac, go to:
Preferences > Advanced > Web Services
and check the option "Use Google Calendar for detected dates."
Disabling Date Detection
In Postbox 6 and beyond, you can disable Date Detection in Preferences (macOS) or Options (Windows) > Display > General.