I see a lot of Node.js modules out there that sends mail through SMTP.
But is there a module to receive mail?
You are looking for an e-mail client library. Currently, there are 2 options (as mentioned here):
I never used them before, but usage is pretty straight forward (according to the docs). node-imap seems to be the more stable library and it has been tested against gmail. If IMAP is an option in your environment, i'd stick with node-imap.
The Mailin module allows you to receive emails, parse them and post them to a webhook of your choice. It is based on simplesmtp. It also checks the dkim and spf, computes a spamassassin score and determines the message language.
Even if it does not fit your needs exactly, you can have a look at the code, it might help you. (Disclaimer: I am the maintainer of Mailin)