Re: Harvest netblocks of good MTAs from SPF for whitelisting from greylisting

On Feb 12, Constantine A. Murenin transmitted in part:

> I'd guesstimate that a setup with pf(4) whitelisting of common MTAs
> through the SPF harvesting approach described, together with
> greylisting at the firewall level, for my domains would be much more
> effective in combating spam than any kind of SPF or DKIM
> implementations at my MTA level, and without the false positives.

But you are doing the same thing as SPF - except guessing the valid MTAs
instead of using the official list conveniently provided in SPF records.
If you are worried about efficiency, SPF records that don't involve
localpart or PTR macros can be resolved to a set of IPs (more general
than a netblock) with a TTL, and cached.  I believe libspf2 has this
feature already.  Take the union of the IP sets of all your "good"
domains if you are going to treat them all the same.