Question about check_sender_mx_access

[Wolfgang Zeikat]

Various sender domains use MX records like mail.spam.domain that point 
to an IP that has a DSL PTR record, like 123-345-78-9.dsl.some.provid.er

Can I catch those using a table entry like
/\.dsl\.some\.provid\.er$/ result
?
Or would I have to use their IP or their A record, e.g. mail.spam.domain?

Regards,

wolfgang