Tell HN: Make sure to configure DKIM/SPF with Fastmail

I've been using Fastmail since 2007, so I haven't touched the DNS of several of my domains in years. All of my email has been getting flagged as spam by GMail recently, and it's likely because I never added DKIM/SPF records to my older domains. I know there are a bunch of old Fastmail users here so figured I'd do a quick PSA