Why does a source fail DMARC, and what does its sentence mean?

On every plan

Each source gets a sentence that says what happens to its mail and why. When something needs fixing, it also gets one action, such as "Turn on DKIM for your own domain in Mailchimp." Expand a source on the domain's Sources page to read both, or open the source's own page.

What the explanation shows

• The case that covers most of the source's mail, with its share, such as "180 of 200 messages", and its sentence. When the source needs attention, the case that needs a fix comes first, however little mail it covers.
• The next largest cases, each with its own count and sentence. Up to four cases show.
• What to do. A case that needs a fix ends its sentence with the action, so each action shows once, under the case it belongs to. The source's action, for its status and its guide link, is the first one its cases ask for, starting from the case with the most mail.

The source's own page adds why we think the source is what it is (see sources) and, when there is an action, a link to the guide for it.

The status beside each source

• Fine: at least 98 percent of its mail passes DMARC.
• Needs attention: less of it passes, and the source is a service we know or sends at least 1 percent of your mail.
• Unknown: less of it passes, and the source is a small one we cannot name.

The actions, and where they lead

Every action is one of these:

• set up DKIM for your domain in the service;
• turn on DKIM for your own domain in the service, in place of the service's own signature;
• turn on custom DKIM and a custom bounce domain in the service;
• say that the service cannot sign mail with your domain, when its own pages describe no setting for it;
• check the DKIM key in DNS;
• fix the SPF record;
• set up the service for your domain, or confirm nobody uses it;
• find out who sends from the source before a stricter policy.

The link goes to the section of that service's own guide when the guide covers the action. Otherwise it goes to the general guide for the action, with the service named in it. For a service that cannot sign, that is the service guide's section on signing with your own domain, or the general section on services that cannot sign. A source whose mail passes needs no action, and when its service cannot sign, its sentence ends with that fact instead.

When the provider's count and ours differ

A report row carries the mailbox provider's own DMARC result and the raw SPF and DKIM results. We work out the result again from the raw results. When the two differ, the provider's result counts, because the provider decided what happened to the mail. The sentence then ends with "We computed a different result from the mailbox provider. The provider's count is what is shown."

Forwarded and mailing-list mail

Forwarding breaks SPF, and a mailing list that changes a message breaks its DKIM signature. When the mailbox provider marks a failure as forwarded mail or as a mailing list, the sentence says so and ends with "Nothing to fix on your side." For forwarded mail, it also says whether the provider delivered the mail, sent it to the spam folder or refused it. The mail left your own systems correctly.

Small and large unknown sources

A source we cannot name, with no SPF or DKIM that passes, gets one of two sentences:

• When it sends at least 1 percent of your mail or at least 50 messages, the sentence says that either a service you use is not set up for your domain, or someone is sending as you at scale. Find out which before a stricter policy.
• When it is smaller, the sentence says that if this is not a service you use, it is someone else sending as you, and a reject policy would stop it.

Old reports get new sentences

We work out the sentence each time you open the page, from the results stored with each report. When we improve a sentence, the improvement reaches every report you already have.

Every case

Here is every sentence a source can get, shown with example.com as your domain and Mailchimp as the service.

Published 27 October 2026 · Checked 27 October 2026