I submitted an application to a company for a software engineering internship, and was contacted by one of their recruiters.
I was interviewed by him on the phone, then scheduled for a technical phone interview, which I passed.
I was then invited on site for 3 1-hour technical interviews, which I passed.
Then I was invited back for a 30-min interview with the head of engineering. He asked me a few questions about scalability of platforms, my favorite platforms, my preference for front-end vs backend, and then asked how much I make per hour at my current job (which is $2/hr more than glass door says their interns make). We finished the meeting, he shook my hand, and 3 days later, I got a no-reply@company.com email stating I had been denied.
What did I do wrong? I'm honestly baffled.
But what really bothers me is that you got a reply from a no-reply address. What the actual fuck. You were there for an on-site interview, this is not the situation where you send people automated no-reply-click-this-link mails.
If their HR doesn't have the time to send a short personal mail (or an automated one from a HR address that doesn't look like it's automated) that might be a red flag on how they treat their employees anyways.
You can try asking them, we at my company were usually happy to tell candidates that didn't pass, why they didn't pass. But we also didn't blow off people with a no-reply mail that were far enough into the process to have been onsite.
The only advice I can give you is to move on and do the next interview. Don't let this get to you.