And, since you’re already looking at the PHPMailer debugging info, you can add this line to lib/pkp/classes/mail/Mail.inc.php
$mailer->SMTPDebug = SMTP::DEBUG_CONNECTION;
Right after this line:
$mailer = new \PHPMailer\PHPMailer\PHPMailer();
in the send()
method.
That should dump out fair amount of debugging information.
Cheers,
Jason