Order confirmations, invoices, download links and quotes that never arrive usually come down to three DNS records: SPF, DKIM and DMARC. Gmail, Yahoo and Outlook.com now filter or reject mail when they are missing or broken. Check your domain free in 10 seconds.
Reads public DNS only, straight from your browser. Nothing is stored and no signup is needed.
Each finding above says what is wrong and what to change. For a worked example, see the fix steps for a real Shopify store: the DMARC record to add, where to click in Shopify, and how to set up DKIM for Google Workspace. Run the check again after each change until everything passes.
A DNS change, a new email tool or a host migration can quietly break SPF or DMARC. The watch re-checks your domain every day and emails you only when something changes. It is free.
Paused for now: the daily re-checks are not running at the moment. You can still sign up, and your first email arrives when they restart.
We use your email only for alerts about this domain. Unsubscribe by replying "stop".
| Mailbox | Rule |
|---|---|
| Gmail | Since February 2024: every sender needs SPF or DKIM. Senders of more than 5,000 messages a day need SPF, DKIM and DMARC. Unauthenticated mail gets rejected with error 550 5.7.26 or goes to spam. |
| Yahoo / AOL | The same requirements since February 2024. |
| Outlook.com / Hotmail | Since May 2025, high-volume senders without SPF, DKIM and DMARC are rejected with error 550 5.7.515. |
| Shopify | If your sender domain isn't authenticated, Shopify rewrites your sender address to [email protected]. Gmail and Yahoo also need a DMARC record, which Shopify doesn't add for you. |
Sources: Google sender guidelines, Microsoft 550 5.7.515, Shopify: setting up your email.
It reads your SPF record and counts its DNS lookups, reads your DMARC policy, looks for DKIM keys under 35 common selectors, and spots Shopify stores whose sender domain isn't authenticated. DKIM selectors can't be listed from DNS. If you use a custom selector, open the headers of an email you sent and look for DKIM-Signature: s= to find it.