SMTP trough Fiddler with Secure traffic Decryption

2 posts, 0 answers
  1. SysTeam DBA
    SysTeam DBA avatar
    1 posts
    Member since:
    Nov 2012

    Posted 05 Jun 2017 Link to this post

    Hi, i'm trying to use Fiddler to test SMTPS communication through a Proxy Tunnel, in the following manner :

    - The client exec an Http Connect command in order to establish a tunnel to the destination SMTP server on port 465.

    - After the connect succeed, the client starts talking with the server through the created tunnel like a normal SMTPS connection.

    This is working successfully if the "decrypt HTTPS traffic" option is disabled.

    When the option is enabled and the interception certificate is created, the client - SMTP communication is shut down all of a sudden.
    After further analysis, it turned out that the SMTP server actually replies correctly to the proxy with the classic "Service Ready" message, but for an unknown reason the message never reach the client (it seem that Fiddler is not passing it to the Proxy-Client connection). So i am wondering if Fiddler applies some kind of filter to Non-HTTP traffic once the decryption is activated. Is this the case ?


    Thank you



  2. Tsviatko Yovtchev
    Tsviatko Yovtchev avatar
    549 posts

    Posted 12 Jun 2017 Link to this post


    Rather unfortunately, fiddler does not really support debugging SMTP traffic. 

    Tsviatko Yovtchev
    Progress Telerik
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