ex < 2013: "Disable Session Limit"=dword:00000001
https://technet.microsoft.com/en-us/library/dd351045%28v=exchg.150%29.aspx
[HKEY_LOCAL_MACHINE\SYSTEM
\CurrentControlSet\Services\MSExchangeIS\ParametersSystem]
"DatabaseType"=dword:00000000
"Maximum Allowed Sessions Per User"=dword:00000080
"Maximum Allowed Service Sessions Per User"=dword:00000080
"Disable Session Limit"=dword:00000001
"DatabaseType"=dword:00000000
"Maximum Allowed Sessions Per User"=dword:00000080
"Maximum Allowed Service Sessions Per User"=dword:00000080
"Disable Session Limit"=dword:00000001
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