From the code qa-include/app/emails.php, it appears Q2A uses PHPMailer.
It does not require a local mail server. But if you select SMTP, then it uses the sendmail binary to send the mail to the configured server.
Check this page for doc and troubleshooting:
GitHub - PHPMailer/PHPMailer: The classic email sending library for PHP
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April 20, 2021: Q2A 1.8.6 released!