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4.2 SMTP Client Not Successfully Authenticating to an SMTP Server

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This section illustrates the NT LAN Manager (NTLM) Authentication: Simple Mail Transfer Protocol (SMTP) Extension with an example scenario in which an SMTP client attempts NTLM authentication to an SMTP server, and the authentication fails.

SMTP client unsuccessfully attempts authentication to SMTP server

Figure 5: SMTP client unsuccessfully attempts authentication to SMTP server

  1. As described in the previous example for unsuccessful AUTH, the SMTP client determines if the server supports NTLM authentication by sending the EHLO command and parsing the EHLO response.

  2. The client sends an SMTP_AUTH_NTLM_Initiation_Command to the server.

     AUTH NTLM

  3. The server sends the SMTP_NTLM_Supported_Response message, indicating that it can perform NTLM authentication.

     334 ntlm supported

  4. The client sends an SMTP_AUTH_NTLM_BLOB_Command message.

     TlRMTVNTUAABAAAAt4II4gAAAAAAAAAAAAAAAAAAAAAFAs4OAAAADw==

  5. The server responds with an SMTP_AUTH_NTLM_BLOB_Response message.

     334 TlRMTVNTUAACAAAAFgAWADgAAAA1goriYo7ENUsXagIAAAAAAAAAAGwAbABOAAA
 ABQLODgAAAA9FAFgAQwBIAC0AQwBMAEkALQA2ADYAAgAWAEUAWABDAEgALQBDAEwASQ
 AtADYANgABABYARQBYAEMASAAtAEMATABJAC0ANgA2AAQAFgBlAHgAYwBoAC0AYwBsA
 GkALQA2ADYAAwAWAGUAeABjAGgALQBjAGwAaQAtADYANgAAAAAA
 

  6. The client then sends an SMTP_AUTH_NTLM_BLOB_Command message. 

     TlRMTVNTUAADAAAAGAAYAHwAAAAYABgAlAAAABYAFgBIAAAACAAIAF4AAAAWABYAZgAAABAAEACsAAAANYKI4gUCzg4AAAAPZQB4AGMAaAAtAGMAbABpAC0ANgA2AHQAZQBzAHQARQBYAEMASAAtAEMATABJAC0ANgA2AIqeV65hhASwAAAAAAAAAAAAAAAAAAAAAHZHDVfwTU5ci0RY04eRmWy0/VWZfIfjsqdUu2WmxYUKy83PyyxzbA8=

  7. The server sends an SMTP_AUTH_Fail_Response message.

     535 5.7.3 Authentication unsuccessful