Domains should not be listed in both "virtual_alias_domains" and "relay_domains" or in both "virtual_mailbox_domains" and "relay_domains".

In the document of Postfix Address Class in http://www.postfix.org/ADDRESS_CLASS_README.html, it explains the address classed that Postfix implement and some of the relationship is illustrated in doc http://www.postfix.org/VIRTUAL_README.html, such as "NEVER list a virtual alias domain name as a mydestination domain!", "NEVER list a virtual MAILBOX domain name as a mydestination domain!", "NEVER list a virtual MAILBOX domain name as a virtual ALIAS domain!".
However, none of these document mentioned that users should NEVER list domain in BOTH "virtual_alias_domains" and "relay_domains", or in BOTH "virtual_mailbox_domains" and "relay_domains". It is better to illustrate these kinds of relationship directly in the document of Postfix Address Class in http://www.postfix.org/ADDRESS_CLASS_README.html, or add some examples in http://www.postfix.org/VIRTUAL_README.html.