Which SMTP mode should we use?

Discussion in 'Installation/Configuration' started by concept21, Jun 5, 2019.

  1. concept21

    concept21 Active Member HowtoForge Supporter

    It is not a bug report.
    I am deploying a new ISPConfig 3.1.13p1 on an Ubuntu 18.04 VM. Postfix runs very well.

    Later, I found this comment in file /etc/roundcube/config.inc.php -
    // SMTP port (default is 25; use 587 for STARTTLS or 465 for the deprecated SSL over SMTP (aka SMTPS))
    $config['smtp_port'] = 25;

    Then, I check my own netstat and it shows that postfix has all of them:

    Now, the problem is - which mode of SMTP should we use when we configure a "send-mail" service? Should we disable TCP port 465 mode? :oops:
  2. till

    till Super Moderator Staff Member ISPConfig Developer

    Port 25 is fine as Roundcube connects on localhost only. if you have other software that runs on the server itself and that connects to localhost, then you can use port 25 for them too. If you connect with other mail clients from external (not localhost), use port 587. Leave the smtps port as it is, it does not hurt to have it.
  3. Jesse Norell

    Jesse Norell ISPConfig Developer Staff Member ISPConfig Developer

    Depending on what you change in your mail system, or what ISPConfig may add in the future, port 587/465 may be better in the future. Eg. I have locally implemented postscreen on port 25, so using one of the other ports is required; hopefully we'll see postscreen as a native option in ISPConfig eventually. Other differences between the ports might exist too, eg. on other (non-ISPConfig) servers we don't allow authentication on port 25 at all, you must submit mail on the mail submission ports, and port 25 has different rate limits/filtering than 587 (I intend to work on our ISPConfig servers with that more in the future, just haven't had time).

    Also fwiw, 465 was deprecated at one point, but is back to being the preferred port for mail submission as of 2018 (rfc 8314), though both 465 and 587 'SHOULD' be implemented.

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