All I found was this SO question using Rails: Email Forwarding like Craigslist - Rails
I googled for a long time but could not find anything using Node.js.
I know this is not the typically accepted SO question, but I literally have no other recourse at this point.
Could you please point me to a resource I could use or some tutorial ? Or maybe you know yourself how to do this ?
EDIT: I ended up using Sendgrid.
In normal cases you have a mailserver that receives the email.
I strongly recommend that you do that, because there are so many things a competent smtp-server handle, that you don't want to re-implement yourself. The smtp-server can then call your program to handle the received mails.
If you really really want to implement a smtp-server for incoming mail in node.js, you can have a look at mailin. It was last updated in August 2017, but have some issues with 2048 bit DKIM keys and some other things.
I have not used it myself, but according to the description it does what you are asking for.