What is “550 5.7.1 – Message rejected as spam”?

You sent an email, and back came a wall of log text ending in 550 5.7.1. The short version: the receiving server looked at your message, decided it was spam, and refused it permanently. No retry will fix it. The underlying cause needs fixing first.

The 550 part means permanent failure. This isn't a "try again in an hour" situation like a 421 (which is a temporary deferral). The 5.7.1 part is an enhanced status code that translates roughly to "delivery not authorized, message refused on policy grounds." What that policy actually is? That's where it gets vague.

Here's the frustrating truth about 5.7.1: it's a catch-all. Receiving servers use it to cover at least five different situations, and they don't always tell you which one. It could be your domain reputation is poor. It could be your IP landed on a blocklist. It could be your SPF, DKIM, or DMARC is failing and the receiving server treats that as a policy violation. It could be your content triggered a spam filter. Or it could be the recipient's admin set a policy that blocks your domain specifically.

The most important thing to read is the full error message, not just the code. Providers like Gmail and Outlook often append a reason or a link to their postmaster documentation right after the 5.7.1. That extra text is your best clue. Don't ignore it.

Once you have the full message, work through this in order. First, check your authentication. Use our free SPF checker and DKIM lookup to confirm your records are passing. A broken SPF record alone can trigger 5.7.1 at some providers. Second, check whether your sending IP or domain is on a blocklist. Our blocklist checker covers the major ones and takes about 30 seconds. Third, look at your content. Spam-heavy phrases, too many links, or a poor text-to-image ratio can all push you over the edge. Fourth, check your sending history. If you recently sent to a cold or old list, that spike in complaints is likely what tripped the filter.

One thing that won't help: suppressing the recipient's address. The rejection here is about your sending reputation or setup, not the recipient's inbox. Removing the address changes nothing. Fix the cause, then resend.

If you've worked through all of that and still can't pinpoint the problem, our SOS hotline is free. Sometimes a fresh set of eyes on your headers makes the difference (and our email header analyzer can help you read them yourself if you prefer).