Exchange 2007
Add-PSSnapin Microsoft.Exchange.Management.PowerShell.Admin;
Exchange 2010
Add-PSSnapin Microsoft.Exchange.Management.PowerShell.E2010;
Exchange 2013 & 2016
Add-PSSnapin Microsoft.Exchange.Management.PowerShell.SnapIn;
Exchange 2007
Add-PSSnapin Microsoft.Exchange.Management.PowerShell.Admin;
Exchange 2010
Add-PSSnapin Microsoft.Exchange.Management.PowerShell.E2010;
Exchange 2013 & 2016
Add-PSSnapin Microsoft.Exchange.Management.PowerShell.SnapIn;