When sending mail via SMTP in Pulse 5.3.11, mail is not delivered. I checked and found that no sender mail is filled in for the SMTP-server. So many SMTP servers will reject the mail.
To make it working, in the file yourdomain.com/inc/tags/form.php. around lines 132:
$mail->From = $sender_email;
$mail->FromName = $sender_name;
$mail->From = \pulsecore\wedge\config\get_json_configs()->json->mail_inputs->Email;
$mail->FromName = \pulsecore\wedge\config\get_json_configs()->json->mail_inputs->Name;
And fill in the sender name and sender email address in the admin section of your pulse site in the forms section, the upper two inputs fields.