Install-Module ExchangeOnlineManagement -Scope CurrentUser

# Exchange Online Modul laden
Import-Module ExchangeOnlineManagement

# Mit dem Microsoft-365-Admin-Konto anmelden
Connect-ExchangeOnline

# ------------------------------------------------------------
# POSTFACH EINSTELLEN
# ------------------------------------------------------------

$Mailbox = "user@firma.de"

Set-MailboxRegionalConfiguration `
    -Identity $Mailbox `
    -Language de-DE `
    -DateFormat "dd.MM.yyyy" `
    -TimeFormat "HH:mm" `
    -TimeZone "W. Europe Standard Time" `
    -LocalizeDefaultFolderName

# ------------------------------------------------------------
# EINSTELLUNGEN KONTROLLIEREN
# ------------------------------------------------------------

Get-MailboxRegionalConfiguration `
    -Identity $Mailbox |
    Format-List

# ------------------------------------------------------------
# VERBINDUNG TRENNEN
# ------------------------------------------------------------

Disconnect-ExchangeOnline -Confirm:$false