had the same problem this happens due to the mailing function beeing blocked to “send as” the email that your applicant provides. it should be easily fixed with an update but i guess no one is looking into it.
in the meantime you can fix this yourself by editing the
getHeader function in the class-job-notifications.php
within that function you can find a bunch of lines constrcuting the email headers for me changing the first two lines fixed the problem
$headers = "From: <[email protected]>\n";
$headers .= "X-Sender: [email protected] \n";
they should look like that just replace the emailadress to the one that wordpress should use to send emails.
be aware that any update to the plugin will revert this file! If they don’t fix the plugin you will have to redo this after each update.