SMTPDummy is a "dummy" SMTP mail server that can be used by software developers for testing email sending software.

SMTPDummy is practical and straightforward, and positively responds to all SMTP commands (i.e., it accepts everything you throw at it), it does not, however, store, forward or sends emails. SMTPDummy does not require installation and is fully portable; you can run it from a USB stick. If does not require configuration, just run the executable and you have a full (albeit dummy) SMTP server.

Its purpose is to merely respond to SMTP commands without functioning as an SMTP server in any way. While it's running, you can see the server's log and the individual messages that it has received. Messages can be displayed as plain text or HTML.

You can use SMTPDummy for debugging your software sending application or for development and integration environments.

Finally, SMTPDummy can listen to any port number (defaults to 25).