And how would php solve the e-mail setup issue? I'm not saying it's straightfoward and I don't know Discourse at all. If they have dependencies like redis etc then yes it's gonna be more complicated. Just don't think a framework like Laravel would have been easier.

Obviously if the project requires working emails, PHP cannot solve it. If I understand the parent comment correctly, what it says is that sending mails with PHP is usually less problematic than other languages (IIRC from the last time that I used PHP -several years ago- their mail() function works OOTB almost everywhere, even on shared hosting, and is usually used by default or as a fallback).