[Exim] How to enable IP MX'es

Hello,

I've got:
all relevant MX records point to non-existent hosts: it
appears that the DNS operator for this domain has installed
an invalid MX record with an IP address instead of a domain
name on the right hand side

I checked that - there is indead IP MX with valid SMTP MTA
on it. Why exim can't use it?

Andrey Novikov