How do I check if my emails are passing SPF, DKIM and DMARC?

Every email you send carries its own test results - you just have to know where to look. Three ways, from quickest to most thorough:

• Read the headers of a real message - send an email to a Gmail or Outlook inbox you control, open the message source ("Show original" in Gmail), and find the Authentication-Results line: it states spf=pass, dkim=pass and dmarc=pass - or exactly which one failed
• Use a mail-testing service - free tools give you a one-time address to email and reply with a scored breakdown of your authentication, useful when you want one shareable report
• Read your DMARC aggregate reports - the only view that covers every service sending as your domain, not just the one message you tested

A single passing test proves the provider you tested from is set up - only the DMARC reports prove the invoicing tool and the contact form are too.