Automatically create SPF records for EC2 instances with static EIP addresses

[gregharvey]

Currently new EIP machines don't get an SPF record for sending email, so any emails go to spam!

This is challenging for a couple of reasons:

• there may be an existing SPF record, so we would have to find that, read it and preserve existing values, appending our own; and
• SPF records do have a length limit of 255 bytes, we'd have to either warn or fail if it was going to be exceeded and not alter the current record

Obviously this is a solution for small usage, where a handful of machines want to send mail. Anything larger will require a custom setup using either macros or subdomains.