Found Here: .net - Authentication failed because remote party has closed the transport stream - Stack Overflow
I came across this issue when trying to send an e-mail to O365 via .NET C# code.
My Option is add the following Registry key:
Key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v4.0.30319
Value: SchUseStrongCrypto
It is worth noting that .NET 4.6 will use the correct protocol by default and does not require either solution.