I know that there are a couple of topics on e-mails not going through, although a couple suggest that there is some custom help that has followed specific to the original poster.
Anyway, I’ve tried quforms with PHP and SMTP both. I’ve tried with various ports and with authentication on and off. I’ve tried using the global setting and also putting a specific setting in quforms and also in the specific form itself. Each time, I do not get an e-mail to send. I’ve also tried with the e-mail address tied to the SMTP account as the reply to address, as opposed to a different e-mail that I’d prefer to use.
My next step was to check in with the hosting company to determine whether there were any issues on their servers or any reason they could determine that would prevent the plugin from working. Wasn’t able to find any reason for a blocker there.