From where do I get the correct syntax to create a proper SPF record for EC2 amazon server? I understand how to create a dns entry but I have no idea what to put in place fo
You can use the Amazon Simple Email Service (SES). If you only use this service (and not directly), then your SPF can be as simple as described in the FAQ:
http://docs.amazonwebservices.com/ses/latest/DeveloperGuide/SPF.html
maybe changing it to a definite fail on mismatch:
v=spf1 include:amazonses.com -all