What Does a 550 5.7.1 Bounce Mean, and How Do I Fix It?

What it means

550 is a permanent failure and 5.7.1 is a generic "not allowed" status. The code alone tells you little: several unrelated problems share it. The text that follows the code is what matters, so copy the full bounce before you change anything.

Because it is permanent, don't keep retrying the same message to the same address. Fix the cause first.

Gmail variants

Google lists these 550 5.7.1 texts in its SMTP error reference, among others:

Google's sender guidelines add one more: a 550 5.7.1 rejection "because the sending server's IP address is on an IP suspended list. You might get this error if you're sending email using a shared IP with a poor reputation."

Microsoft 365 variants

Microsoft says 5.7.1 "indicates a security setting in your organization or the recipient's organization is preventing your message from reaching the recipient." For cold senders the variants that matter are:

• "Client host [xxx.xxx.xxx.xxx] blocked using Blocklist 1": your sending IP is on Microsoft's blocklist. Forward the bounce to delist@microsoft.com or use the delist portal.

• "Delivery not authorized" or a group that accepts only members: a recipient-side restriction. Microsoft notes that "Typically, you can't fix the problem yourself." Remove the address from the campaign.

• "Unable to relay" or "Client was not authenticated": a configuration problem on the sending or receiving server, usually an MX or relay setting.

Microsoft also uses its own codes for newer rules, such as 5.7.515 for failed authentication. See Outlook blocking cold email.

Yahoo

Yahoo describes its permanent errors as 553 and 554. Its error code page lists invalid addresses, failed DMARC or DKIM, content policy and a Spamhaus listing of your IP among the causes, and says not to retry an email that comes back with a 5xx error.

554 5.7.1

The same 5.7.1 status also comes with a 554 reply code, mostly from servers other than Gmail and Microsoft 365. The two common texts:

• "Relay access denied": the server that answered does not accept mail for the recipient's domain. Usually the domain's MX record points to a host that no longer handles its mail, or the company moved its email. Microsoft describes the same case under "Unable to relay": "An MX record for a domain points to a receiving email system where that domain isn't accepted." Look up the recipient domain with MX lookup; if the mail moved or the company closed, remove the contacts.

• "Service unavailable; Client host [IP] blocked using" a list name: the receiver checked a blocklist and found your sending IP on it. Check the IP and domain with the email blacklist check and ask your mailbox provider about the IP.

The email bounce decoder reads the text after either code and says which case you have.

What to do

1. Group your bounces by code and by exact text.

2. If most say reputation or unsolicited mail, check whether a neutral email from the same mailboxes is also refused or sent to spam. If yes, the problem is in the IPs or the domain.

3. If the text names headers, PTR or authentication, fix the setup. These are not reputation problems.

4. Remove addresses that return recipient-side restrictions.

5. Watch the bounce rate per mailbox for a few days after the fix. See bounce rate too high.

Questions

What does a 550 5.7.1 "rejected for policy reasons" bounce mean?

The receiving server's own policy refused the message, and texts such as "this message does not meet our delivery requirements" or "permanently rejected - policy violation" don't say which rule you broke. The causes this code covers include failed authentication, a sending IP or domain on a blocklist, and content or sender history judged as spam. Paste the bounce into the email bounce decoder, check the domain and IPs with the email blacklist check, and send a neutral email from the same mailbox to see whether the copy is the cause. Don't retry the same message to the same address.

What does "your access to submit messages has been rejected" mean in Office 365?

It is a 5.7.1 rejection from a Microsoft 365 or Exchange server, and Microsoft says 5.7.1 means "a security setting in your organization or the recipient's organization is preventing your message from reaching the recipient." If the bounce also says "blocked using Blocklist 1", your sending IP is on Microsoft's blocklist: forward the bounce to delist@microsoft.com or use the delist portal. Otherwise the recipient's organization restricts who can send to it, which you usually can't fix yourself, so remove the address from the campaign.

Why was my email rejected with 550 5.7.1 as spam?

The receiving filter judged the message, its sender history or a link in it as spam. Gmail's version reads "This message is likely unsolicited email"; texts such as "recipients have complained about included content" or "rejected as spam by content filtering" point at the copy or a URL in it. Send a neutral email and your campaign email from the same mailbox: if only the campaign email is refused, rewrite it and remove links and tracking. If both are refused, the sending IPs or the domain are the cause; cold email infrastructure covers a setup on separate domains with warmup on every mailbox.

What we recommend at Outreach2day

We set up SPF, DKIM and DMARC on every domain automatically. That removes the authentication causes. The reputation causes remain, which is why we recommend up to 25 cold emails per mailbox a day and warmup for every mailbox.