I'm trying to make sure a user types in a valid email that also actually exists, not just valid in format. There is a npm package called email-existence that should do this but every email returns a false so that is not reliable. If there is a javascript/Node.js Package that does this job, it would be great, but is there also a way I can do this myself? Like ways to create a small module for this functionality?
The only guaranteed way to find out whether an e-mail address exists is to send an e-mail to it - this is why verification e-mails exist.
There's a similar discussion here with a few answers detailing possible ways to try and determine if an address exists on a server, but none are guaranteed to work on every server.
Alternatively, you could use a paid service such as Kickbox.io (they also have a 100/day free quota), which claims to verify that an e-mail address exists as well as determine the "quality" (based on deliverability and other metrics) of an address. Kickbox has a node.js package.