Mailnag is a daemon program that checks #POP3 and #IMAP servers for new mail.
On #mail arrival it performs various actions provided by plugins.
#Mailnag comes with a set of desktop-independent default plugins for
visual/sound #notifications, script execution etc. and can be extended
with additional plugins easily.

https://github.com/pulb/mailnag

GitHub - pulb/mailnag: An extensible mail notification daemon

An extensible mail notification daemon. Contribute to pulb/mailnag development by creating an account on GitHub.

^GitHub