Insert Job Details into E-Mail

Hi,

I want to add some job details to the notification email like this:

function my_sjb_applicant_details_notification( $message, $post_id, $notification_receiver ){

    $message .= '<p><b>Category:</b> ';
    $jobpost_categories = get_the_terms( $post_id , 'jobpost_category' );

    $i = 1;
    foreach ( $jobpost_categories as $category ) {
        $message .= $category->name;
        $message .= ($i < count($jobpost_categories))? ", " : "";
        $i++;
    }
    $message .= '</p>';

    $message .= '<p><b>Type:</b> ';
    $jobpost_job_types = get_the_terms( $post_id , 'jobpost_job_type' );
    $i = 1;
    foreach ( $jobpost_job_types as $job_type ) {
        $message .= $job_type->name;
        $message .= ($i < count($jobpost_job_types))? ", " : "";
        $i++;
    }
    $message .= '</p>';

    $message .= '<p><b>Location:</b> ';
    $jobpost_locations = get_the_terms( $post_id , 'jobpost_location' );
    $i = 1;
    foreach ( $jobpost_locations as $location ) {
        $message .= $location->name;
        $message .= ($i < count($jobpost_locations))? ", " : "";
        $i++;
    }
    $message .= '</p>';

    return $message;

}

add_filter( 'sjb_applicant_details_notification', 'my_sjb_applicant_details_notification', 10, 3 );

I already found the filter “sjb_applicant_details_notification”, but the $post_id is the ID of the applicant and NOT the job ID.

Where is the applicant ID linked with the job ID in the database?
I couldnt find anything in wp_postmeta.

Thanks!
Jan