Share Exchange Resources with external users

This guide describes how to share resources from your own environment with external persons (e.g. partners or office members). Internal persons can be invited or adapted in the same way. However, these instructions refer to collaboration outside the company.
Sign in to Exchange Online
The settings are only available via PowerShell and cannot be found in the Exchange Admin Center (WebGUI). Accordingly, you need the PowerShell module “ExchangeOnlineManagement”.
Install PowerShell module
Open a new PowerShell window with administrator rights and execute the installation command:
Install-Module -Name ExchangeOnlineManagement -Force
Connect to Exchange Online
You must then open a new PowerShell session. This should not have administrator rights and must be started from scratch (do not use an existing window, as the available module paths are not loaded correctly there).
Import-Module ExchangeOnlineManagement
Connect-ExchangeOnline
A browser pop-up will then appear. Follow the instructions and log in with your administrator account. The user should have Exchange Admin permissions.
This module contains many functions for the Sign In options. You can find more information here: Connect to Exchange Online PowerShell | Microsoft Learn
Get folder settings for calendar
This command displays all settings. Here you can check the current status of the configuration and your subsequent adjustments.
Get-MailboxCalendarFolder -Identity <youremailadress>:\calendar
Share calendar state publicly
This command configures the external sharing of calendar availability. The corresponding HTML and iCAL links are then displayed in the overview (execute the previous command again). Look for the parameters "PublishedCalendarUrl" & "PublishedICalUrl".
Set-MailboxCalendarFolder -Identity <youremailadress>:\calendar -PublishEnabled $true
Set shared details for calendar events
The availabilities are now displayed on the ICAL and HTML accesses by default. More details are not available. You can change the DetailLevel to these three settings so that external persons receive more or less information about the calendar.
AvailabilityOnly (default)
LimitedDetails
FullDetails
Set-MailboxCalendarFolder -Identity  <youremailadress>:\calendar -DetailLevel LimitedDetails
Allow external calendar booking
With this command you can allow the booking of external mail addresses. If this is executed, all mail requests for resource accounts are answered and a confirmation mail is sent back if available. Take care to only enable this feature on calendars that are intended to be public.
Set-CalendarProcessing -Identity <youremailadress> -ProcessExternalMeetingMessages $true