SPF

While normally SPF means Sun Protection Factor for me, I have to say, as Sender Permitted From, I am delighted by the headers.

Set in the DNS, SPF headers tell mail servers what IP addresses and hostnames email can actually be sent from. Receiving mail servers can check that incoming email is originating from those allowed servers, and reject (or discard) emails that aren't originating from authorized servers. The latter being likely spam, though sometimes misconfigured email servers, as I had with my Shopify store until I realized what I had done.

Checking out the mail logs and seeing these messages come across delights me:

Recipient address rejected: Message rejected due to: SPF fail - not authorized. Please see http://www.openspf.net/Why?s=mfrom;id=auto-shipping@amazon.com

Fuck you spammers. You make the internet a less lovely place to be.