New-Mailbox `
  -DisplayName "AD-DisplayName" `
  -Name "AD-Name" `
  -FirstName "Vorname" `
  -LastName "Nachname" `
  -OrganizationalUnit "distinguishedName of OU" `
  -UserPrincipalName "AD-Username" `
  -SamAccountName "AD-SamAccountName" `
  -LinkedCredential $credential `
  -LinkedMasterAccount "dom\samaccountname" `
  -LinkedDomainController "dc" `
  -alias "mailboxalias" `
  -Database Databasename `