SMTP Error 550: No Such User Here means the recipient’s mail server could not find the email address you are trying to send to.
This guide will help you:
- Understand why the error occurs
- Identify the exact cause
- Fix the issue quickly
- Restore successful email delivery
In most cases, the problem is simple to resolve and does not affect your website, hosting account, or domain functionality.
By the end of this guide, you’ll confidently diagnose and resolve SMTP 550 errors without unnecessary support escalation.
What SMTP Error 550 Means
SMTP Error 550 is a permanent delivery failure (hard bounce).
This means the recipient server rejected the message and will not retry delivery automatically.
Common error examples include:
550 No Such User Here
550 Invalid Recipient
550 User Unknown
550 Mailbox Unavailable
550 Recipient Not Found The receiving mail server indicates that the mailbox does not exist or cannot be located.
Why This Matters
Ignoring 550 errors may lead to:
- Emails permanently failing
- Broken communication with clients
- Mailing list delivery failures
- Confusion over bounced messages
Correctly identifying the cause ensures the email can be delivered successfully.
Step-by-Step Fix for SMTP 550 Error – No Such User Here
Follow these steps in order.
1: Confirm the Full Error Message
Open the bounce notification and confirm it includes variations such as:
550 No such user here
550 Invalid recipient
550 User unknown
550 Mailbox unavailable If a different SMTP code appears, refer to the SMTP Error Codes guide.
2: Verify the Recipient Email Address
Check the recipient’s address carefully.
Common mistakes include:
- Spelling errors
- Missing characters
- Incorrect domain names
Example:
[email protected] instead of [email protected] Correcting the address often resolves the issue immediately.
3: Confirm the Mailbox Exists
If the email is sent to your own domain:
Log in to:
If the mailbox does not exist:
4: Check Email Routing Configuration
Incorrect email routing can cause servers to reject valid users.
Log in to:
- cPanel → Email Routing
- Plesk
Confirm the setting is correct:
- Local Mail Exchanger → if email is hosted locally
- Remote Mail Exchanger → if using Google Workspace or Microsoft 365
Incorrect routing often occurs after domain migrations or hosting changes.
5: Review MX Records
Incorrect MX records can direct email to the wrong server.
Check the DNS records by using a DNS lookup tool to verify:
- MX records point to the correct mail server.
If incorrect:
- Update the MX records in your domain DNS settings.
DNS changes may take time to propagate.
6: Check Email Forwarders
Misconfigured forwarders can cause mailbox lookup failures.
Check:
- cPanel → Email Accounts → Forwarders
- Plesk → Mail → Forwarding
- Confirm forwarders point to valid addresses.
- Remove any invalid or outdated forwarders.
7: Contact the Recipient
If all checks are correct on your side, the issue may be on the recipient’s server.
Ask the recipient to:
- Verify their mailbox exists
- Confirm the correct email address
- Contact their hosting provider if necessary
Then, resend the message.
8: Review Delivery Logs (Basic Level)
Log in to:
- cPanel → Email → Track Delivery
- Plesk → Websites & Domains → Select your domain → Mail → Track Email Delivery
Then:
- Observe retry attempts and timestamps
Quick Fixes for Common SMTP 550 Variations
SMTP 550 errors are permanent rejections, meaning the message cannot be delivered until the issue is corrected.
1. 550 No Such User Here
Example:
550 No such user here
550 User unknown
550 Recipient not found What It Means:
The recipient email address does not exist on the destination server.
How to Fix It:
- Verify the spelling of the email address
- Confirm the mailbox still exists
- Ask the recipient to confirm their correct email
This error only affects the specific email message.
2. 550 Invalid Recipient
Example:
550 Invalid recipient
550 Address rejected What It Means:
The email address format or domain may be incorrect.
How to Fix It:
- Check spelling and formatting
- Ensure the domain is correct
- Remove outdated addresses from mailing lists
3. 550 Mailbox Unavailable
Example:
550 Requested action not taken: mailbox unavailable What It Means:
The mailbox may have been removed, disabled, or not yet created.
How to Fix It:
- Ask the recipient to verify the mailbox exists
- If this is your domain, create the mailbox in your hosting panel
Creating or correcting the mailbox usually resolves the issue.
Advanced (Optional) Fixes (For Technical Users)
Administrators, or Technical Users, can diagnose mailbox lookup failures and server-level issues using server logs and command-line tools.
1. Check Mail Server Logs
Inspect SMTP transaction logs to determine why the mailbox lookup failed.
Common log locations:
/var/log/exim_mainlog
/var/log/maillog Search for rejection messages:
grep "550" /var/log/exim_mainlog Look for:
- User lookup failures
- Routing errors
- Invalid mailbox entries
2. Verify Mailbox Configuration
Confirm that the mailbox exists in the mail server configuration.
Check mailbox directories:
/home/username/mail/domain.com/ If the mailbox directory is missing, recreate the account in the hosting panel.
3. Inspect DNS MX Records via CLI
Verify MX configuration using:
dig MX domain.com 4. Check Forwarders and Aliases
Verify alias configuration files:
/etc/aliases
/etc/valiases/domain.com Invalid or broken aliases may trigger user lookup errors.
5. Validate Email Routing
Check Exim routing configuration:
exim -bt [email protected] This command shows how the mail server attempts to route the message.
Misrouted domains can cause mailbox lookup failures.
Before You Move On
- Confirm the recipient address is correct
- Ensure the mailbox exists
- Verify email routing configuration
- Confirm MX records point to the correct mail server
If This Didn’t Work
Try to confirm the following:
- Send the message from another email account
- Verify MX records using a DNS lookup tool
- Check forwarders and aliases
- Confirm the recipient mailbox still exists
If the issue persists, contact support with:
- Full bounce message
- Timestamp of the email
- Sender address
- Recipient address
Common Mistakes to Avoid
- Sending to outdated mailing list addresses
- Using incorrect domain names
- Migrating hosting without updating MX records
- Incorrect email routing after domain migration
Empowering Insight
Most SMTP 550 errors are caused by simple address errors or deleted mailboxes.
Verifying the recipient address usually resolves the problem within minutes.
Next Recommended Steps
Learn how to improve email deliverability:
- Understanding SMTP Error Codes
- Configure SPF, DKIM and DMARC
- Troubleshooting Email Delivery Failures
FAQs
Q. Will this affect my website?
No, this error only affects the specific email message being sent.
Q. Can I try resending the email?
You can resend the email after correcting the recipient’s address or mailbox issue.
Q. Does this error mean that my domain is blacklisted?
No, this error indicates a mailbox lookup failure, not a blacklist issue.
Additional Resources
SMTP Error Codes
SPF/DKIM Setup Guide
Email Sending Limits Guide
Email Bounce Back Guide
Need Additional Support?
We’re Here to Help:
Understanding SMTP Error 550 and how to fix this doesn’t have to feel technical with this easy-to-reference guide. Stuck? Check out our Scope of Support, and then contact our Support Team for further clarity and guidance (https://1grid.co.za/contact-us/). We’re ready to see how we can help!