fo tag
The DMARC tag choosing when failure reports should be generated: 0, 1, d, s or a combination; it is ignored if ruf is absent.
What it means
fo=0 (the default) requests a report only when every mechanism fails to give an aligned pass, which is when DMARC fails. fo=1 requests one when any mechanism fails to give an aligned pass, even if DMARC passed through the other. fo=d requests a DKIM failure report for any signature that failed to verify, aligned or not, and fo=s an SPF failure report for any SPF failure.
Values combine with colons, such as fo=1:d, but 0 and 1 cannot be used together. Receivers may choose not to follow the request.
fo=1 is the most useful setting for troubleshooting, since it reports partial failures before they become DMARC failures.
Example
v=DMARC1; p=none; ruf=mailto:dmarc-failures@example.com; fo=1Related terms
Sources
What this definition rests on. The wording is ours; the facts are theirs.
All 432 terms in the glossaryThe wiki: blocklists and bounce codes