What is DMARC alignment (relaxed vs strict)?

DMARC alignment is the check that the domain a recipient actually sees in the From field matches the domain that passed SPF or DKIM - because an email can pass those tests for a different domain than the one it claims to be from:

• Why alignment exists - SPF checks the hidden envelope sender and DKIM checks the signing domain; alignment ties either result back to the visible From address.
• Relaxed alignment - the default; the organisational domain must match (mail.yourbusiness.com.au aligns with yourbusiness.com.au), which suits most senders using third-party tools.
• Strict alignment - the domains must match exactly, with no subdomains allowed; tighter, but it breaks easily when you send through external services.
• The practical default - relaxed alignment is right for nearly every small business; strict is for tightly controlled sending only.

DMARC only passes when at least one of SPF or DKIM both passes and aligns - alignment is the link that makes authentication meaningful.