I've found this wonderful explanation of SPF on http://www.openspf.org/SPF_Record_Syntax and i had it working on my older setup.
Setup has changed and i find myself in the ropes again.
I have an external DNS service. A router on a dynamic IP connection. A server with a 10.0.1.3 internal ip. DNS records on this server, stating that server.example.com points to 10.0.1.3. I use the server dns to resolve its own and local network queries. I also have an app installed to send my external DNS service updates if the router ip changes.
What i've figured out so far is that in this particular case i might be able to successfully use an TXT record along the lines of
"v=spf1 a:server.example.com -all"
Would this work? Assuming the ip doesn't change exactly when the email is sent... What would be the best way to go about setting this up?
PS. I my understanding i might be able to use "v=spf1 mx -all" and have my server.example.com as an mx record, and in turn server.example.com dynamically updating to my ip when it changes. This way when some receiver get's an email from my ip... this checks the MX record to see if the ip is in that list, then it gets server.example.com as the response which in turn always resolves to my latest dynamic ip.