SMTPRelay is a Relay or Proxy Server for sending email, and was born of the need to send email from a PC that is not connected to the Internet, but is a member of a private network with access to the Internet. Email packets are directed from the machine without access to one with access, which simply relays those packets to the SMTP server of your choice and routes returning packets back to the original machine. To the outside SMTP server, it looks like the packets originated from the intermediate relay machine.

SMTPRSvc.exe is an executable designed to run as a service. There is no visible forms or controls, and the SMTP Server, the Listening Port, and the SMTP Connecting Port are all defined in the Registry. When installed as a Service and started, it is quite likely that the Operating System will not prompt you to update the Windows Firewall to allow access. To facilitate this, simply run the executable directly. Since there is no visible interface, you will have to use the Task Manager or reboot the system to shut the program down.

SMTPRCrtl.exe does have a visible interface, and is used to manage the Service component. It will Install/Uninstall the service, Start/Stop the service, and Setup the Registry values. Because it is accessing System only values, it must be run in Administrative Mode.

There is not much to look at because this program runs as a service.

The management program shown above simplifies the installation and management of the service. However, once the service has been installed and setup, the Service Manager (services.msc) can be used to manage the service. Using the Service Manager, you can change the StartUp Type to Automatic from Manual, so that the service will start at bootup.

To test SMTP Relay, go to another machine on the local network and direct your email program to the machine running SMTP Relay. The Relay program will contain the name of the SMTP Server normally used. Send an email to yourself and verify that you received it. SMTP Relay is not designed to use cryptographic protocols such as SSL/TLS.

Note: SMTP Relay uses IP Version independent system calls that support both IPv4 & IPv6. Therefore, it will only work on Windows Operating Systems that support dual stack, and this more or less restricts it to Windows Vista or better. SMTPRelay is written in VB6, and is being made available in ZIP format. Installation is usually straight forward, using "setup.exe" to install files extracted from "SMTPRelay.cab" as laid out in "setup.lst".

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