I solved the bug by adding the following to the main.cf:
relay_domains =
The problem was caused by relay_domains autoamtically matching subdomains of $mydestination for backwards-compatibility, which I did not know about.
I solved the bug by adding the following to the main.cf:
relay_domains =
The problem was caused by relay_domains autoamtically matching subdomains of $mydestination for backwards- compatibility, which I did not know about.