permit_mx_backup_networks uses the same parser as mynetworks, and therefore it expects the same main.cf syntax as mynetworks.
In smtpd_check.c:
mynetworks =
namadr_list_init(match_parent_style(VAR_MYNETWORKS),
var_mynetworks);
...
perm_mx_networks =
namadr_list_init(match_parent_style(VAR_PERM_MX_NETWORKS),
var_perm_mx_networks);
> [2001:6f8:128a::1]/128 # dict_open: unsupported dictionary type: [2001:
This does not reproduce here with:
permit_mx_backup_networks = [2001:6f8:128a::1]/128
Wietse
