ALIASDOMAIN.TAB

 "aliasdomain"[TAB]"realdomain"[NEWLINE]

where 'aliasdomain' can use wildcards:

 "server.org"   "server.com"
 "*.xserver.net"   "xserver.net"

The first line defines 'server.org' as an alias of 'server.com' while the second remaps all subdomains of 'xserver.net' to 'xserver.net'.

You 'CANNOT' edit this file while AfterLogic XMail Server is running because it is an indexed file.