While I used to think Railway was an amazing service, I had a production workload get broken because they removed a feature without any depreciation period or warning. I now struggle to recommend it for anything more than a hobby project. Vercel has the benifit of being big enough they have to do things properly. For reference https://station.railway.com/questions/smtp-connection-failur...

SMTP is gated behind the $20/mo Pro plan to reduce spam on the internet.

It sounds like you were running a production workload on the Hobby plan