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What does this error message mean?
Your email came back with a code like «550 5.7.26»? Paste the message here. You will learn in plain words what is probably going on and what you can do.
Not transmitted and not stored: the analysis runs only in your browser.
The explanation lists possible causes, not a diagnosis. The recipient’s information is what counts.
Is it your domain?
Many rejections are related to SPF, DKIM or DMARC. The free domain check shows within seconds how your domain is set up. In DomainRadar, the explanation appears right next to the status of your domain.
Rule table 2026.10.1, as of 2026-10-11.