Because, nowadays, we require relay hosts in the internal network to
hold a valid certificate before we accept their relayed mail.
I don't know why chiark is included in the list.
## Other hosts allowed to relay mail through us.
DEFCONF(relay_clients, <m4_dnl
## Other hosts allowed to relay mail through us.
DEFCONF(relay_clients, <m4_dnl
; 172.31.80.8 m4_dnl chiark (VPN)
; 172.31.80.8 m4_dnl chiark (VPN)
-; 172.29.198.161 ; 2001:8b0:c92:a000::1:1 m4_dnl national