This is a follow-on to the question "How can I add an email alias to a domain alias in Google Apps?"
A primary domain has been successfully set-up with Google Apps (not G Suite) e.g. domain1.com
A secondary domain alias to the primary domain has also been setup. It has been verified e.g. domain2.com.
Although I successfully receive an email that is sent to email@example.com, the error message "A delivery loop was detected which causes this email to be undeliverable" is received when an email is sent to firstname.lastname@example.org.
It has been 24 hours since the domain alias was added.
Is there any additional step that must be completed?