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It is possible that in cloud-based systems – for example in Microsoft Azure – port 25 is blocked by the provider. However, port 25 is required to send emails, which prevents the operation of NoSpamProxy on such a system. We offer an alternative to use such systems anyway: our “TCP Proxy”. This system can be activated in NoSpamProxy as described below. Then the emails are sent from the server via port 443 to the TCP Proxy and from there via port 25 to the recipient system.

General information on using the TCP proxy

  • If the TCP proxy is implemented, it appears as the sending system. Therefore, the TCP proxy must also be included in your SPF record using
  • You must download the certificate mentioned below and import it into the Microsoft certificate management system of the computer account on the system with the NoSpamProxy gateway role as a “Trusted Root Certificate”.

Integrating the TCP Proxy

  1. Stop the service of the gateway role via the NoSpamProxy console or the Windows services.
  2. Open as administrator a text editor on the system on which the gateway role is installed..
  3. Open the configuration file “Gateway Role.config” from the directory “C:\ProgramData\Net at Work Mail Gateway\Configuration\”.
  4. Look for <smtpServicePointConfiguration in the file. If you cannot find <smtpServicePointConfiguration, alternatively search for <netatwork.nospamproxy.proxyconfiguration and add the following line directly below: <smtpServicePointConfiguration isProxyTunnelEnabled="true" />
  5. Save the file and close the editor.
  6. Place the root CA certificate in the Microsoft certificate store in the computer account under “Trusted Root Certification Authorities > Certificates” on the server where the gateway role is located.
  7. Edit the corresponding gateway role in the NoSpamProxy console under “Configuration > NoSpamProxy components > Gateway roles” and change the value for “SMTP server name” to the “”.
  8. Start the gateway role service again.
  9. Open the file “Gateway Role.config” again and check whether the value was retained at startup.