This guide will demonstrate how to share your default calendar between users in SmarterMail:
First, you will need to share your calendar under "Settings"
Under "Sharing" select "Shared Resources" and hit the "New" button.
From here select the "My Calendar" radio button and hit "Next":
The next page will allow you to choose specifically who can share the calendar with you:
After hitting "Save" the user that needs to share your calendar will need to login and go to their settings.
Under "Mapped Resources" they will need to select your now visible calendar and hit "Attach":
Your calendar will now be visible under this users calendar section.