SMTP Error 550

An email error code indicates an unsuccessful email transaction between the sender and recipient’s server. 

SMTP error 550 is one of such errors that suggests your recipient’s server bounced your incoming message.

What Does SMTP Error 550 Mean?

In simplest terms, the 550 error message means the receiver’s mail server blocked your message and sent it back to you. 

Unlike the SMTP 554 error caused by the recipient or sender’s server, the 550 email error is often caused by the recipient’s server. 

The 550 error code message has different variations. Decoding them is the first step to fixing the issue. Here are examples of some common ones:

  • SMTP Error 5.5.0
  • 550 User account is unavailable
  • 550 No such user here
  • Remote host said: 550 —, this domain [recipient’s domain] Mailbox Does Not Exist — Giving up
  • does not like recipient

Remote host said: 550-Verification failed for

550-Previous (cached) callout verification failure

550 Sender verification failed. Giving up on

Although you might see these messages above (or a variation of them), you can also see a 5.1.0 error message that looks like this:

5.1.0 – Unknown address error 550-‘Mailbox is inactive’

This occurs when a recipient’s server is down due to a system-wide problem.

Now you know how a basic 550 error message looks like, let’s go on to what causes this error and how to fix it.

What Causes a 550 Error and How to Fix it?

There are a few reasons why you could be receiving SMTP Error 550. The most common cause is that the receiving email server has rejected your email for one of the following reasons:

1. Invalid Recipient Address

This occurs when there’s a typo in the recipient’s email address or extra spaces. Ensure that you have the correct email address from the recipient, or make sure you typed in the correct characters.

If this doesn’t solve it, it could be that you have the wrong email address, or the recipient now uses a different domain or new address.

2. Bad Domain Reputation

This means the recipient’s server doesn’t trust the domain name you are using. If this happens, then your email IP is blacklisted, and your messages will bounce. 

Reasons for this could be your system has a virus or malware, and:

Someone is exploiting a webmail app’s vulnerability and uploading a spam script.

Or, that person has access to your account and is using it to send spam messages. 

Either way, to fix this, you’ll need to check if your IP address is blacklisted and send a delist request from the public RBL database.

Another option is to install malware scanners on your system. This will scan outgoing emails and alert you if your email account is compromised. While you’re at it, notify our support team of the issue immediately.

3. Server Downtime 

The receiving email server is currently not available due to a planned downtime or some technical problems. If it’s urgent, request an alternative email or try resending your email after a few hours.

4. Email Policy Violation

Sometimes, the recipient’s server may be blocking your message due to an email policy violation. You’ll need to ensure you have everything fixed on your end. Do away with bulky attachments, spam words, and bad headers, as these are common policy violations for major email providers.

If you’re not sure, read the email policy of your email service provider.

5. Bulky Messages

The receiving email server might block a message when it’s too bulky. You could split your messages into parts and send them separately or compress your attachments into a zip file.

6. Bad DNS Records

When this happens, it means your mail server has a mismatch of DNS records, or there is no available reverse DNS record for your IP address. 

This error is depicted with the message: “550 reverse DNS”. Please contact us to reconfigure your SMTP server configurations and check your DNS records.

7. ISP Restriction

The network administrators (those who manage ISP servers) place restrictions on mail servers that often carry spam messages. 

When the junk email from a specific SMTP server increases, it blocks it to prevent spam on their network. Contact your ISP providers to resolve this issue.

8. Compromised SMTP Port

Since spammers often use port 25 to send spam messages, the recipient’s server can block your email if it uses the same mail port. 

Change the port to 2525, 26, 887, or 465, and see what happens.

These errors and fixes above are not exhaustive, but these are the common ones you should be able to fix quickly. We also recommend that you update your passwords regularly and use email security software to prevent outsider access to your email account.

Need Help?

Now you understand the SMTP Error 550, you might need any help with any thing related to the points we discussed here. If that’s the case, please contact our support at any time. We are available, around the clock.

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Working in the web hosting industry for over 13 years, Rado has inevitably got some insight into the industry. A digital marketer by education, Rado is always putting himself in the client's shoes, trying to see what's best for THEM first. A man of the fine detail, you can often find him spending 10+ minutes wondering over a missing comma or slightly skewed design.