Recently a friend asked me about SPF and DKIM. I was vaguely aware of them and their generally perceived uselessness. I've never bothered with them but thought I'd look into them for him. SPF was trivial to set up using my Bytemark DNS, and easy to testing using of many on-line email tools.
The challenge is DKIM, I found several sites that explained what to do - they were all variation around a theme and seemed easy enough. Generate a key pair (check), put the public half into your DNS (check), tweak Exim4 (ARGH!!!).
As far as I tell I followed what the web site said and reloaded the Exim config and it looks like it's all loaded into place, the key is readable by Exim, the path is correct but no matter what I do Exim wont add the DKIM signature to my outgoing emails...!