[exim] Throttling mail based on MX record

Hello all,

I'm currently throttling mail using the following setup:

domainlist throttled_domains = yahoo.com : yahoo.co.uk : yahoo.ca :
yahoo.es yahoo.it

# This router limits the messages per outbound SMTP conenction:
throttled_out:
driver = dnslookup
domains = +throttled_domains
transport = smtp_throttled
ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8
no_more

smtp_throttled:
driver = smtp
max_rcpt = 9
connection_max_messages = 5

What I'd also like to do is to limit max_rcpt based on the MX of the
recipient. Something along the lines:

hostlist throttled_mx = mx1.domain.com : mx2.domain.com

And with a condition in a new router (forgive my pseudo-code):

condition: if lookup $recipient_mx in $throttled_mx then true


Is this possible ?

TIA,
Marius