[exim] message_size_limit depending on incoming domain

Hi,

I know that there is a setting message_size_limit and that I can
control it
globally and per router.

I accept mails for a lot of domains and for some of those domains
I'd like to
have a bigger message_size_limit than for the rest. Those domains
are already
handled differently but I am not sure at which point the
message_size_limit
comes into play.
In acl_check_rcpt I have several rules regarding those domains.
Can I do in one of
them something like

accept  domains       = 
partial-lsearch;/usr/local/etc/exim/conf/special_domains
          local_parts   = 
          nwildlsearch;/usr/local/etc/exim/conf/special_accounts/$domain
          set SPECIALDOMAIN = true
          endpass

or

warn  domains = 
partial-lsearch;/usr/local/etc/exim/conf/special_domains
        local_parts = 
        nwildlsearch;/usr/local/etc/exim/conf/special_accounts/$domain
        set SPECIALDOMAIN = true
        set acl_m0 = 3
        set acl_m1 = 1
        set acl_m4 = 1

(those are the existing rules, just with 'set SPECIALDOMAIN =
true' inserted)


and then write in the global-setting
.ifdef SPECIALDOMAIN
message_size_limit = 100
.else
message_size_limit = 50
.endif


or is acl_check_rcpt too late in the configuration for the
message_size_limit-check?
If it is so, I guess I have to allow generally the big mails and
then create
routers that deny the big mails for everyone except those in the
special
domains, right?

Cheers,

Niels