These e-mails are sent from an automatic sender: The email address may be masked to appear like it is being sent from a different address, this is called spoofing.  If the email address is being spoofed the receiving email servers (applicants) may not allow this email to be received. The email may not show in the applicant's spam or junk mail folders as the mail server filters it before it is delivered.

This may be resolved by your applicant requesting their IT department to whitelist on the mail server.