If your domain is verified and emails are being sent successfully, but internal systems (like Microsoft Exchange) are flagging them as external:
This is typically related to your company’s internal email rules, not Nectar.
For example, In Microsoft Exchange Admin, navigate to Mail Flow > Rules
Find and click rule that is marking / prepending emails as external.
Note: If you’re following this example replace
em[0-9]+.nectarhr.com with the similar value from one of the generated DNS records. In this guide our generated value was
em3065.nectarhr.com