SPF and DKIM Alignment: What are they and why do they matter?

If you have implemented DMARC for your email sending domain, the spec requires that your messages either pass "SPF alignment" or "DKIM alignment." Here's what those are and why they are important (and why you should always do both).

SPF alignment is where the mail you send has a return-path domain (aka the sender domain or bounce domain) that matches your from address domain. A DMARC record uses the "aspf" setting to govern how tightly this is checked. If you do not include the "aspf" setting (and you don't need to), then the default "relaxed" setting will be applied.