ex < 2013: "Disable Session Limit"=dword:00000001
https://technet.microsoft.com/en-us/library/dd351045%28v=exchg.150%29.aspx
[HKEY_LOCAL_MACHINE\SYSTEM
New-ThrottlingPolicy AllMailboxViewer
Set-ThrottlingPolicy AllMailboxViewer -RCAMaxConcurrency Unlimited -EWSMaxConcurrency Unlimited -EWSMaxSubscriptions Unlimited -CPAMaxConcurrency Unlimited -EwsCutoffBalance Unlimited -EwsMaxBurst Unlimited -EwsRechargeRate Unlimited
Set-Mailbox "User Name" -ThrottlingPolicy AllMailboxViewer