RE: do you use SPF TXT RRs? (RFC4408)

how many of you are using SPF records? Do you have an opinion on their use/non use of?

We use SPF on most client domains. On inbound filtering, we add no score for a lack of SPF record, and we reject mail if the SPF record hardfails. We've seen it reduce domain-imposter spam. It's not the ultimate spam fighting tool, but it does give you some control over your own domain for whoever will listen to it, which is handy. The only 'DoS Mitigation' I can think of is that the presence of a hardfail record would help keep your domain off the various DBLs. You could call "getting a domain blacklisted" a denial of service, I suppose. Nathan