You are free to do whatever you want, but why not explain in your contributing guidelines that this is how you operate?
https://github.com/nodemailer/nodemailer/blob/0b78689e5a8641... The text starts with:
"First, thank you for considering contributing to nodemailer! We welcome any type of contribution, not only code. You can help with
QA: file bug reports, the more details you can give the better (e.g. screenshots with the console open)"
It is completely is incongruent with what you have written here. Again, your project, your time, but this is almost tricking people into expecting something that they shouldn't expect. Personally, I have no problem with maintainers using stale bots, but please tell me about it so I can avoid wasting my time on those projects.