Telnet using AUTH NTLM to exchange 2013

I am trying to test NTLM Authentication on our Exchange 2013 environment and I am unable to get the correct Base64 command for passing the username and password to the server. I have been doing the following

telnet IP Address 25

receive the expected response

helo

receive the expected response

AUTH NTLM

334 NTLM Supported

I then attempt to put in a Base64 string wich is converted from 'domain\username password'. I think this is where I am going wrong but I cannot find anything useful on how the string should be formatted or converted. Any help will be most appreciated