Confirm the provider accepted it
Check that the source mailbox received the test and that its forwarding rule is enabled. Some providers require a separate confirmation before forwarding begins.
Check address and loops
Compare the forwarding destination character for character and remove rules that send mail in a circle. Use a new subject because providers may group or suppress repeated tests.
Collect safe evidence
Record sender domain, recipient mailbox, subject, and approximate time without sharing message secrets. Check spam or provider rejection notices before contacting support.