Wildcards for MX and CNAME in same zone - allowed?

[Van Bemmel, Berend]

Dear All,

For a zone hosted through an ISP I was requesting to put in two wildcard
records, one for the MX and one for  a CNAME, e.g.

*	MX 10		mailhost.example.com.
*	CNAME		www.example.com

Now my ISP tells me they can not do this because a zone file can only
contain one wildcard entry, so I had to choose to either use the wildcard MX
or the wildcard CNAME, both they refused to do. 

I fail to see the reasoning behind this since MX and CNAME are different
request types.

Can somebody tell me if my ISP is right or that I should pursue the matter
further with them.

Thanks for any help you can provide,

Berend