Status_203 - 8:48 am on Sep 16, 2011 (gmt 0)
DKIM = Yet another pile of esoteric technology that I had to use (in some way) if I wanted people with yahoo email address to be able to register to use my tools!
Actually, my sunconcious has obviously been mulling this over for the last day I've got vague memories of the initial bouncing being related to switching forum software.
I emailed all currently active users ( I think it was approx 30 at the time!) that I was changing software, that the tools would be down on such and such a date, and if they couldn't log in when they were back up to let me know.
With the way my server was set up at the time I think it took only 6(!) identical emails to Yahoo addresses without DomainKeys for them to blacklist my web server as an email sender!