550 5.7.1 (and its cousin 554 5.7.1) means the receiving server refused your message on purpose, for a security or policy reason. Unlike 550 5.1.1, the address usually exists: the server simply decided not to accept mail from you, or not this message.

This is the code with the most possible causes, so the text that comes after it matters more than the code itself. This page shows how to read it and what to do in each case. For every other code, see our guide to SMTP bounce codes.

What the code means

  • 550 / 554: a permanent failure ("mailbox unavailable" / "transaction failed").
  • 5.7.1: "delivery not authorized, message refused". The .7 means security or policy.

So it is a permanent refusal, but it is about you or your message, not about the address. Removing the address from your list does not fix it.

Read the text after the code

The receiving server almost always explains itself in the words after the code. The common families:

What the text says What it usually means
"blocked", "listed", a blocklist name or a link to a delisting page Your sending IP or domain is on a blocklist the receiver uses.
"likely unsolicited", "spam", "content rejected" Spam filtering judged the message (or your recent mail) as unwanted.
"relay access denied", "not permitted to relay" The server was asked to pass the message on to another domain and refused. Usually a configuration problem on the sending side.
"sender rejected", "not authorized to send" The sender address or domain is refused, often by a rule the recipient's admin set up.
"message does not pass authentication" / DMARC Authentication failed: see 550 5.7.26.

With Google Workspace recipients, a 5.7.1 can also come from a custom rule set by the recipient's administrator (for example, only accepting mail from certain domains). Then only that administrator can change it.

How to fix it

1. Check whether your IP or domain is blocklisted. Free blocklist lookups such as MXToolbox check the main lists at once. If you are listed, find out why (a compromised account, a bad list, a spike in complaints), fix it, then request removal on the list's own site. Removal without fixing the cause usually does not last.

2. Check your authentication. SPF, DKIM and DMARC should all pass and align with your From domain. Our SPF and DMARC checker and DKIM checker show what is missing.

3. Look at what you sent. Spam filters weigh complaints, sudden volume spikes and content. Sending to a cold, old or bought list is the fastest way to get a 5.7.1: it brings bounces, spam traps and complaints together.

4. If it says "relay denied", your mail server or app is trying to send through a server that does not accept you as a client. Check the SMTP settings (server, port, authentication) of the tool that sent the message.

5. If only one company refuses you, contact that company another way and ask them to allow your domain. Some organisations block all mail from outside a list of approved senders.

How to prevent it

  • Keep your list clean. Invalid addresses, spam traps and abandoned mailboxes are what push senders onto blocklists. Verify lists before sending, and check them again if they are a few months old; MailQuell also flags spam-trap risk signs such as domains on spam blocklists, brand-new domains and parked domains.
  • Warm up new domains and IPs slowly instead of sending thousands of messages on day one.
  • Make unsubscribing easy so people do not use the spam button instead.
  • Follow the sender requirements of Gmail, Yahoo and Outlook.

Frequently asked questions

Is 550 5.7.1 a hard bounce?

It is a permanent refusal, but not an address problem. Do not delete the address because of a 5.7.1: fix the reason, and the same address will accept your mail again.

What is the difference between 550 5.7.1 and 554 5.7.1?

Very little in practice. Both are permanent policy refusals; servers pick one or the other. Read the text after the code.

Why do only some of my emails get 5.7.1?

Policies are often applied per receiver or per message: one company's filter, one blocklist used by some providers but not others, or one campaign's content. Look at which domains refuse you.

Sources