You can share your appointments with internal as well as external partners. Depending on the requirements, different methods exist.
To make a calendar available for internal users or external partners, proceed as follows:
Create a new personal or public calendar folder.
You can also share an existing folder.
If another internal user shared a calendar folder with you, you can access this folder in the folder tree.
To invite external partners to an appointment, proceed as follows:
When creating the appointment, add external partners as external participants.
Make sure the Notify all participants by E-Mail option is enabled.
The external partner receives an e-mail with an appointment invitation in iCal format. Information can be found in Viewing Appointments