An SMTP and POP3 server for local testing of email services.
You may build the application from source, or download a pre-built version from the App Store.
When first launched, the application displays a window with buttons to create a new mail store, load saved mail store definitions, and delete the current mail stores.
Creating a new store adds a server block to this window: 
While the servers are stopped, you may change the ports on which the SMTP and POP3 servers will listen. Obviously, these can't be changed while the servers are running.
Stumpy is distributed under the terms of the MIT License. It is written in Swift, based on the architecture of dumbster.