Why business emails go to spam — in plain words
Inboxes now check who you are
Gmail requires every sender to pass SPF or DKIM, and anyone sending around 5,000 messages a day to Gmail must also publish DMARC. Yahoo applies the same rules, and since May 2025 Outlook.com rejects failing high-volume mail with error 550 5.7.515. Mail that can’t prove where it comes from is the first to land in spam.
The three records, without jargon
SPF is a guest list: the servers allowed to send email for your domain. DKIM is a wax seal: a signature showing the message wasn’t forged or changed. DMARC is the instruction to inboxes: what to do with mail that fails both — deliver, send to spam, or refuse.
Why it matters beyond spam
Without a DMARC policy that quarantines or rejects, anyone can send an email that appears to come from your business — a fake invoice to your customers, a payment request to your bookkeeper. Getting this right protects the people who trust your name.
What this check can’t see
Authentication is necessary, not sufficient. Your sending reputation, complaint rate, list quality and message content also matter, and only the mailbox providers see those. The check looks for DKIM under the names providers commonly use; a key published under an unusual name may not be found.
Sources
- Email sender guidelines — Gmail Help
- Email sender guidelines FAQ — Gmail Help
- Sender best practices — Yahoo
- Outlook’s requirements for high-volume senders — Microsoft
- RFC 7208 (SPF) and RFC 7489 (DMARC)