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297680Postfix smtp via socks5

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  • Francina Oates
    Jan 24, 2014
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      I was trying to send using default transport/smtp through a socks5 proxy provided by ssh -D.

      I experience Postfix does not easily supports this, but I got pretty far:

      a. Install tsocks package on Ubuntu 13.04

      b. Create /usr/lib/postfix/smtp_socks
      #!/bin/bash
      export TSOCKS_CONF_FILE=/etc/postfix/tsocks.conf
      exec tsocks /usr/lib/postfix/smtp "$@"

      c. Create /etc/postfix/tsocks.conf
      server = 127.0.0.1
      server_port = 1126
      server_type = 5

      d. Add to /etc/postfix/master.cf
      smtp_socks unix - - - - - smtp_socks

      e. Add to /etc/postfix/main.cf
      default_transport = smtp_socks

      f. Set up tunnel and send email to the Internet
      ssh -D 1126 remoteserver.com

      It does not work:
      smtp does not actually create connections but more likely hands that off to some other process.
      The log displays:
      postfix/smtp[7848]: connect to aspmx.l.google.com[2a00:1450:4008:c01::1a]:25: Network is unreachable
      postfix/smtp[7845]: connect to aspmx.l.google.com[74.125.25.27]:25: Connection timed out

      Of course this works:
      TSOCKS_CONF_FILE=/etc/postfix/tsocks.conf tsocks telnet aspmx.l.google.com 25
      Trying 173.194.79.27...
      Connected to aspmx.l.google.com.
      Escape character is '^]'.
      220 mx.google.com ESMTP g6si6607378pad.169 - gsmtp

      As opposed to blocked while not using socks5:
      telnet aspmx.l.google.com 25
      Trying 173.194.79.27...
      ^C



      How can I make it work?


      There are great reasons for using a SOCKS5 server:
      - perhaps your computer has a dynamic ip
      - perhaps your isp does not allow port 25 connections
      - perhaps you want an encrypted connection all the way to the recipient's mta, as opposed to have an unencrypted mail queue somewhere on the Internet

      We do NOT want an intermediate mta or postfix.

      Looking forward to any suggestions,

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