outlook.com keeps sending me dmarc reports with failed dkim... while every single other provider gives pass to all domains. at this point I don't even care anymore.
They have a crappy internal DNS caching server in the email infra that times out early and returns NXDOMAIN for timeouted requests, causing permfail for DKIM instead of tempfail as RFC suggests in case of DNS timeouts. This crap has been going on for years.