Stop outbound SMTP TLS connections falling back to non-TLS


SUMMARY

You may need to configure the mail server to not fall back to non-TLS connection if the TLS connection fails. By default, when sending an email, the SMTP service will try to use TLS if the remote server supports it. If the TLS connection fails, the SMTP service will instead try to send non-TLS. This article describes how to change that behaviour and make those emails bounce.

DETAIL

You will need to enable the registry key below as described below:

  1. Open Microsoft Windows "regedit".
  2. Navigate to the following MailEnable registry branch:

    32bit Windows: HKEY_LOCAL_MACHINE\SOFTWARE\Mail Enable\Mail Enable\Connectors\SMTP

    64bit Windows: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Mail Enable\Mail Enable\Connectors\SMTP

  3. Create a new DWORD key named: No TLS fallback
  4. Set the decimal value to: 1
  5. Close "regedit"
  6. Restart the SMTP connector


    Product:MailEnable
    Article:ME020704
    Module:General
    Keywords:
    Class:HOWTO: Product Instructions
    Revised:Sunday, February 23, 2020
    Author:
    Publisher:MailEnable