wp-includes/PHPMailer/PHPMailer.php:1008Send messages using qmail.
public function isQmail() { $ini_sendmail_path = ini_get('sendmail_path'); if (false === stripos($ini_sendmail_path, 'qmail')) { $this->Sendmail = '/var/qmail/bin/qmail-inject'; } else { $this->Sendmail = $ini_sendmail_path; } $this->Mailer = 'qmail'; }Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/PHPMailer/PHPMailer.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.