You might wonder why you would need to set something up while in comparison PHP’s mail command works out of the box with no special configuration whatsoever. Just call mail(...) and you’re already sending mail. So what’s going on in Node.js?
The difference is in the software stack required for your application to work. While Node.js stack is thin, all you need for your app to work is the node binary, then PHP’s stack is fat. The server you’re running your PHP code on has several different components installed. Firstly the PHP interpreter itself. Then there’s some kind of web server, most probably Apache or Nginx. Web server needs some way to interact with the PHP interpreter, so you have a CGI process manager. There might be MySQL also running in the same host. Depending on the installation type you might even have imagemagick executables or other helpers lying around somewhere. And finally, you have the sendmail binary.
What PHP’s mail() call actually does is that it passes your mail data to sendmail’s stdin and thats it, no magic involved. sendmail does all the heavy lifting of queueing your message and trying to send it to the recipients’ MX mail server. Usually this works because the server is an actual web server accessible from the web and has also gathered some mail sending reputation because PHP web hosts have been around for, like, forever.
Node.js apps on the other hand might run wherever, usually on some really new VPS behind an IP address that has no sending reputation at all. Or the IP is dynamically allocated which is the fastest way to get rejected while trying to send mail. So while you might actually emulate the same behavior with Nodemailer by using either the sendmail transport or so called direct transport, then this does not guarantee yet any deliverability. Recipient’s server might reject connection from your app because your server has dynamic IP address. Or it might reject or send your mail straight to spam mailbox because your IP address is not yet trusted.
So the reason why PHP’s mail works and Node.js’s does not is that your PHP hosting provider has put in a lot of work over several years to provide a solid mail sending infrastructure. It is not about PHP at all, it is about the infrastructure around it.