This looks correct, but I may be wrong
#################################
.ifdef HIDE_MAILNAME
#################################
.ifdef HIDE_MAILNAME
-REMOTE_SMTP_HEADERS_REWRITE=*@+local_domains $1@DCreadhost frs : *@ETC_MAILNAME $1@DCreadhost frs
-REMOTE_SMTP_RETURN_PATH=${if match_domain{$sender_address_domain}{+local_domains}{${sender_address_local_part}@DCreadhost}{${if match_domain{$sender_address_domain}{ETC_MAILNAME}{${sender_address_local_part}@DCreadhost}fail}}}
+REMOTE_SMTP_HEADERS_REWRITE=*@+unix_domains $1@DCreadhost frs : *@ETC_MAILNAME $1@DCreadhost frs
+REMOTE_SMTP_RETURN_PATH=${if match_domain{$sender_address_domain}{+unix_domains}{${sender_address_local_part}@DCreadhost}{${if match_domain{$sender_address_domain}{ETC_MAILNAME}{${sender_address_local_part}@DCreadhost}fail}}}
.endif
.ifdef REMOTE_SMTP_HELO_FROM_DNS
.endif
.ifdef REMOTE_SMTP_HELO_FROM_DNS