Don't use an external domain, just forward jobapplication@employer.com to incoming@applicantfilter.com and have it forward only the approved applications to hr@

Don't use an external domain, just forward jobapplication@employer.com to incoming@applicantfilter.com and have it forward only the approved applications to hr@employer.com. Fully automated and transparent. Store the rejected applicants and send them an automated "thanks for your time" when the position is filled.