Specify path to Blocked Senders list
Supported on: At least Windows Server 2008 R2 or Windows 7
Registry
HKCU
software\policies\microsoft\office\16.0\outlook\options\mail Options
junkmailblockedsendersfile text Description
Specify a text file containing a list of e-mail addresses to append to or overwrite the Blocked Senders list (depending on the policy "Overwrite or Append Junk Mail Import List").