[Exim] dnslists acl wishlist

I just read the spec and there's something I'd like exim to beable to do.

I've been looking at RBLs and notice some use different A records depending
on the type of block they do.  Most of the ones I come across I'd like to
block all but 1 type.  For instance:
    dnslists = dnsbl.sorbs.net!=127.0.0.8

What do others thing of this? (I'm willing to code it if I can understand
the code well enough)

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