SMTP error 550: What it means and how to fix it
SMTP error 550 overview:
- The 550 error is permanent: You need to fix the cause before delivery will succeed.
- Start with the basics: Confirm the recipient address, then check SPF/DKIM/DMARC.
- Reputation matters: Blocklists and poor sender reputation commonly trigger 550 rejections.
SMTP error 550 is a permanent failure code that indicates the recipient’s email server has rejected your message. Unlike temporary errors (4xx codes), a 550 bounce means you need to take action before your email can be delivered.
Use Sendmarc’s enterprise-grade email security platform to strengthen authentication and improve sender visibility, so you can avoid the common misconfigurations that trigger permanent rejections.
What SMTP error 550 means
When you receive a 550 error, the recipient’s email server is telling you: “I’m rejecting this message permanently.” The server won’t retry delivery, and the email will bounce back.
The 550 code falls under the “5xx” category of SMTP response codes, which all indicate permanent failures. The 5 means the error is fatal, so the message won’t be delivered unless the underlying issue is resolved.
Common causes of SMTP error 550
Provider-specific 550 errors
Google (Gmail, Google Workspace)
| Error message | Meaning |
|---|---|
| 550 5.1.1 – The email account that you tried to reach does not exist | Invalid recipient address |
| 550 5.7.1 – Our system has detected that this message is likely suspicious | Content flagged as spam |
| 550 5.7.1 – Unauthenticated email from example.com is not accepted due to domain’s DMARC policy | DMARC check failed |
| 550 5.7.26 – Your email has been blocked because the sender is unauthenticated | Missing authentication |
Microsoft (Outlook.com, Hotmail, Live)
| Error message | Meaning |
|---|---|
| 550 5.7.1 – Unfortunately, messages from [x.xx.xx.xx] weren’t sent | IP is on a blocklist |
| 550 5.7.515 – Access denied, sending domain example.com does not meet the required authentication level | Authentication insufficient |
Exchange Online Protection (Microsoft 365)
| Error message | Meaning |
|---|---|
| 550 5.7.606 – Access denied, banned sending IP | Domain blocklisted |
Yahoo (Yahoo, AOL, Verizon)
| Error message | Meaning |
|---|---|
| 550 – Relaying denied | Domain not hosted at Yahoo |
iCloud (icloud.com, me.com, mac.com)
| Error message | Meaning |
|---|---|
| 550 5.1.1 – <[email protected]>: user does not exist | Invalid recipient |
| 550 5.7.1 – Message rejected due to local policy | Policy-based rejection |
| 550 5.7.1 – Your message was rejected due to example.com DMARC policy | DMARC authentication failure |
Yandex
| Error message | Meaning |
|---|---|
| 550 5.7.1 – Policy rejection on the target address | User agreement violations |
| 550 5.7.1 – No such user! | Invalid address |
How to fix SMTP error 550
Step 1: Verify the recipient address
Start with the basics. Double-check the email address for:
- Typos in the username or domain
- Extra spaces or special characters
- Outdated addresses
If you’re sending to a list, remove invalid addresses to protect your sender reputation.
Step 2: Check your email authentication
Most 550 errors related to authentication stem from missing or misconfigured records. Verify your:
SPF record:
- Ensure your sending IP or service is included in your SPF record
- Check that you haven’t exceeded the 10 DNS lookup limit
- Verify the SPF record syntax
DKIM signature:
- Confirm DKIM is enabled for your sending domain
- Validate that the DKIM public key is published in the DNS
DMARC policy:
- Ensure SPF and DKIM are fully configured first
- Review your DMARC alignment settings
Step 3: Review your sender reputation
Poor reputation is also a cause of 550 rejections. Check your status:
- Blocklists: Use a blocklist checker to see if your IP or domain is listed
- Google Postmaster Tools: Monitor your domain reputation
- Microsoft SNDS: Check your IP reputation using Microsoft
If you’re blocklisted, follow the provider’s delisting process.
Step 4: Contact the recipient or their admin
The recipient’s IT team may have specific policies blocking your messages. They can:
- Add your domain or IP to their allowlist
- Adjust their filtering settings
How email authentication prevents 550 errors
Many 550 errors occur because receiving servers can’t verify you’re a legitimate sender. Proper email authentication tells recipient servers that your emails are genuine.
SPF
SPF lets you specify which email servers are authorized to send messages on behalf of your domain.
Example SPF record:
| Host | Type | Value |
|---|---|---|
@ | TXT | v=spf1 ip4:192.168.0.1 include:mail.example.com -all |
DKIM
DKIM adds a digital signature to your emails to verify the message wasn’t altered in transit.
Example DKIM record:
| Host | Type | Value |
|---|---|---|
selector._domainkey.yourdomain.com | TXT | v=DKIM1; k=rsa; p=[public key] |
DMARC
DMARC ties SPF and DKIM together and tells receiving servers what to do when authentication fails. It also provides visibility into sending activity.
Example DMARC record:
| Host | Type | Value |
|---|---|---|
_dmarc.yourdomain.com | TXT | v=DMARC1; p=reject; rua=mailto:[email protected]; fo=1; |
Protect your domain with Sendmarc
A misconfigured sender, shadow SaaS tool, or compromised mailbox can lead to fraud, brand damage, and delivery issues. Sendmarc helps security and IT teams gain centralized visibility and control over email authentication – while reducing manual effort.
- Reduce impersonation risk: Enforce DMARC and monitor unauthorized domain use
- Improve inbox delivery: Identify misconfigured senders and fix them early
- Prove compliance: Generate board-ready reports and maintain audit trails
- Lower operational load: Centralize SPF/DKIM/DMARC visibility and decrease investigations
- Implement safely: Roll out in stages and optimize continuously
See what’s happening across your domains. Identify gaps, prioritize fixes, and reduce avoidable rejections.
SMTP error 550 FAQs
What is the difference between a 550 error and a 450 error?
A 550 error is a permanent rejection – the receiving server refused the message, so it won’t be delivered unless the underlying issue is fixed. A 450 error is a temporary deferral – the receiving server couldn’t accept the message right now, and the sending server will usually retry later.
Can I resend an email after getting a 550 error?
Resending an email after a 550 error usually won’t help unless you fix the underlying cause first. A 550 rejection can be triggered by issues like an invalid recipient address, missing authentication, or sender reputation problems, so the email is most likely to be rejected again until that issue is resolved.
What are the most common causes of 550 errors?
The most common 550 error causes include: Invalid recipient addresses, blocked IPs/domains, authentication failures (SPF/DKIM/DMARC misalignment), and content/policy rejections.