RLetters is open-source software, released under the terms of the MIT License. While it was until recently hosted at GitHub, the source code repository can now be found at Codeberg. Feel free to visit there to check out the source, report bugs, or submit a patch.
Below you can find some further documentation that might be of interest if you’re working on the code. It specifies various quirks or details that we’ve worked out over the life of the project.