I've set up a contact form and use Nodemailer to send emails through the app/api directory. It works smoothly in dev and when I test the build locally, but the Vercel deployment won't send any mails. I've looked through the interwebs and found more people having the same issue, but no solution yet. I know the code is working, as I've even set up a transport.verify() function in the file that logs success in the vercel deployment log (see image).

The only documentation I've found at Vercel is this:
https://vercel.com/guides/sending-emails-from-an-application-on-vercel

I can't (and do not want) to use a thrid party service for this, but for me at least it seems like they say it's possible to do this "on your own", using Nodemailer. The one thing I'm a bit confused about in the docs above is this statement here:
When doing so, we recommend using an external host value provided by a third-party provider, rather than defaulting to the outbound SMTP connection of the Serverless Function.

How do I know if I'm "...defaulting to the outbound SMTP connection of the Serverless Function." ?

My current route.ts code is in the other image, and as mentioned works fine in dev.

Anyone that could help me out here? All help and tips are highly appreciated.