Microsoft Exchange | Shell | OWA Calendar sorting week numbers

In Europe and USA there are different types how the first week of the year is count.

There are several types of counting them –> https://de.wikipedia.org/wiki/Woche#Kalenderwoche

In Exchange the default sort is like the US system. If you want to change them to a different sorting follwing steps in Exchange Management Shell are needed:

Check the current value:

Get-MailboxCalendarConfiguration User | fl FirstWeekOfYear

First Day = US count type

FirstFourDayWeek = Europe count type

Change from US to Europe type:

Set-MailboxCalendarConfiguration -identity User -FirstWeekOfYear FirstFourDayWeek

Now the first Week in Calendar should have been changed. But only for one user. 

With this script at every User Mailbox this will be set: 

foreach ($Mailbox in (Get-Mailbox -ResultSize Unlimited)) { Set-MailboxCalendarConfiguration -identity "$($Mailbox.Name)" -FirstWeekOfYear FirstFourDayWeek }