Laravel Symfony Mailer: Unable to Connect with STARTTLS Due to Peer Certificate Hostname Mismatch (HIN.CH SMTP)

Email is an important part of modern web apps, and Laravel makes it easy by including the powerful Symfony Mailer. However, developers sometimes have trouble setting up SMTP services. One of these common mistakes is

"Can't connect to STARTTLS because the peer certificate hostname doesn't match."

When using secure SMTP providers like HIN.CH, this problem often happens. In this article, we'll explain what caused this error and show you how to fix it in Laravel step by step.