Frequently Asked Questions

In the most basic sense, an email error message means that the receiver's email hosting server blocked the email you sent, and as a result, was returned to you.
While the message might seem cryptic to ordinary eyes, it is decodable and can help in reaching the root of the problem.

What causes email error 550?

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The email error message is linked to the Simple Mail Transfer Protocol (SMTP), which is a set of standardised rules to send and receive emails. And so, it is also known as SMTP 550 error code. In some cases, email error 550 is caused by a problem at the recipient's side.
Here are some possible causes for email error 550:

1. Your email address has been compromised and so is blocked by the recipient's mail server.
2. The recipient's email address doesn't exist.
3. The recipient's email address is temporarily unavailable or suspended.
4. The recipient's hosting server is temporarily unavailable.
5. Your domain name is invalid or blocked.
6. Your internet gateway has a firewall or a filtering feature which mistakenly identified your email as spam and blocked it.
7. Your email is mistakenly identified as spam by the recipient's mail server.
8. You are using your email client from a different IP address.

Common phrases denoting email error 550

1. Email Error 550 5.1.0 Address Rejected

This error message means the recipient's server won't accept emails from you. This is most probably because the recipient blocks your email address.

2. Email Error 550 5.1.1

This error message means the recipient email address you entered is invalid or doesn't exist in the destination domain. It happens either because of email address typos or due to a misconfiguration of the recipient's server.

3. Email Error 550 Denied By Policy

It means an email security software has blocked outbound emails to prevent attackers from guessing addresses by sending randomly generated email addresses.

4. Email Error 550 5.4.1

This error message means the recipient's server doesn't accept emails from the domain you use. A DNS misconfiguration generally causes this error.

5. Email Error 550 5.7.0 Message Size Violation

This error occurs when your email has a file exceeding the size limit.

6. Email Error 550 5.7.1 Access Denied

This error message means the email was rejected either because of security policies or incorrect configuration on the recipient side.

7. Email Error 550 Administrative Prohibition

This error message will mean any of the following:

• The domain used by your SMTP server is on Real-time blacklists.
• The recipient uses a domain that is on Real-time blacklists.
• The SMTP server has a dynamic IP address.
• The recipient's mail server failed to identify your email address. 

8. Email Error 550 Relay Not Permitted

It means the recipient's server does not permit the server you are using to send the email.

9. Email error 550 Quarantined / 550 Error Recipient Quarantined

It means your email was flagged as spam and wasn't delivered. You will face the same error message if your email address is blacklisted.

10. Email error 550 SPF

A mail server will check the Sender Policy Framework (SPF) record of a domain to verify whether a sender is valid or not. While sending email from an IP address not recorded in SPF, you will receive this error message.

11. Email error 550 reverse DNS

It means there is no Reverse DNS record for the mail server's IP address or there is a mismatch of records in the domain used to send the email.

12. Email error 550 recipient unknown / no such user here

This error message means the recipient's mail server is unable to find the mail account. This can happen due to email address typos.

13. Email error 550 host unknown

The SMTP server sends this message if the hostname specified in the email address is unknown.

14. Email error “550 Authentication is required for relay”

It means that the Simple Mail Transfer Protocol (SMTP) authentication is missing. In order for you to send outgoing mail, SMTP authentication should be enabled on your email client, with your username and password.

15. Server error 550 or 550 Blocked Error

Requested action not taken error message pops up when the email you’re trying to send was blocked by the email hosting server of the recipient. This SMTP error code indicates the email will be redirected back to the sender.

16. Error 550 #5.1.0 Address Rejected

This message indicates the recipient's server won't accept emails from sender (you) or recipient’s messages. This error pops out if your email address or any (if not all) Exchange Online emails are blocked by the recipient.

17. Server error “550 this domain is not hosted here”

This is another common error. The email being sent is rejected by the server when the recipient's username is not found or is inaccessible. Other reasons include typo errors in the email address and incorrect MX records directing to the wrong server.

18. Error 550 in Outlook

This error message is often associated with 550 Authentication is required for relay. It means your email server needs SMTP authentication to send out emails, but the email client used is yet to be authenticated with your username and password.

How do I fix a 550 error?

1. Check for email address typos

Email Error 550 can occur due to typos in an email address. Make sure the email address you entered is correct, and there are no extra spaces or misspellings. There are also chances for the recipient to have given you the wrong email address. Confirm with them as well.
Along with that, check whether your email address is entered correctly and your email has contents in it. Some mail servers will reject an email having no content in it.

2. Check whether the email IP is blacklisted

If your email IP is blacklisted in a DNS blacklist, most of your emails won't reach the recipient and will bounce instead.
Image Credits: leadfuze.com
If your email IP is blacklisted, it means either:

• Someone exploited the webmail application's vulnerability and is uploading a spam script into it.
• Someone has access to your email account and is using it as a tool to send out spam messages.

Along with these, different blacklist databases have different criteria for flagging an email IP. So, it is best advised to find the database to analyse your options.
You can check whether your email IP has been blacklisted here.
Once you find the blacklist database, you can move ahead with removing your email IP from the blacklist.

3. Try sending the email after some time

There are chances that the recipient's server is temporarily down due to several reasons. Inform the recipient that the server may be down, and ask for an alternative email address or wait for a few minutes or hours till you try again.

Speaking of time, you can also check out this post to find out the best time to send an email.

4. Try changing your outgoing mail port

If your email application uses port 25 as an outgoing mail port, there are chances for servers to block the email as spammers use port 25 often to send spam messages. Try changing your port to 26, 465, 587 or 2525.

 Image Credits: serversmtp.com
If you are using a firewall, you will have to verify the change in port to allow traffic to pass.

5. Check whether IP filtering is enabled

Your SMTP server may be set up to authorise users from only a specified set of IP addresses. If that's the case, you won't be able to send messages from other locations. You can quickly resolve this by contacting the admin of your mail server.

6. Enable SMTP authentication

In most email applications, the SMTP authentication is automatically configured. In case, the application fails to configure it; you won't be able to send emails. Luckily, you can configure SMTP manually.
If you are using Mozilla Thunderbird, follow these steps.
Image Credits: support.mozilla.org

1. From the top menu, click on Tools and select Settings.
2. Under Settings, select Outgoing Server (SMTP) and click Edit.
3. Choose the SMTP server you wish to configure and click Edit.
4. Check or add your username and password.
5. Click OK.

If you are using Outlook, follow these steps.
Image Credits: support.icewarp.com

1. Click on File Tab and select Account Settings.
2. Verify and select your email in the Email Tab and click on the Change icon above it. The Internet Email Settings open.
3. Click on the Outgoing Server Tab.
4. Now, make sure the box “My outgoing server (SMTP) requires authentication” is ticked and “Use same settings as my incoming mail server” circle-box is selected.
5. Click OK followed by the Finish button.

Do note that the steps to enable SMTP authentication will differ depending on the email application you use.

7. Troubleshoot the SSL method

As discussed, a majority of email clients use an auto detect feature to set up SMTP. While setting up SMTP manually, there will be several combinations of SSL available, including:

1. None
2. STARTTLS
3. SSL/TLS

During manual setup, you will need to verify the SSL method used by the SMTP server and configure the email client subsequently.

8. Contact your ISP

If the above solutions fail to resolve your issue, then it's advised to contact your Internet Service Provider for assistance. There are chances that your ISP's filtering system might be blocking your email.

How to prevent email error 550?

1. Scan outgoing emails

Email error 550 can occur if your email account is compromised and is used by spammers to send spam messages. By default, anti-spam systems scan all incoming emails. To make sure your account is not misused, set-up anti-spam systems to scan outgoing emails as well.

2. Scan for malware on file uploads

If your account is compromised, attackers will use it to send spam messages along with files containing malware. To prevent it, set up malware scanners to automatically scan each file uploaded.

3. Block direct outgoing connections to SMTP servers

Spam scripts might try to connect with remote SMTP servers directly. By blocking such connections, emails can be sent only through mail servers - making it easier to monitor per user email volume, and take measures if anything suspicious arises.

4. Limit the number of emails per hour

Generally, an email user will need to send a maximum of 50 emails per hour. So, it is advised to limit the number of emails sent per hour to 50 or lower, depending on your usage. This will significantly reduce the damage a spammer can cause.

5. Use a web application firewall

Firewalls can protect your system from attackers exploiting the vulnerabilities of web apps. This will ensure your account stays protected from spammers as well.

6. Change password

It is best advised to change your passwords frequently. Also, make sure your passwords have nothing related to your name, age or date of birth. Combine letters, special characters and numbers to make it more enduring.

Conclusion

As you can see, email error 550 may or may not be easily resolvable, depending on its cause. Email errors can happen even if your recipient's inbox is full. Also, with several hackers trying to exploit vulnerabilities of email applications, it is best advised to use email security software and change your passwords consistently.

It’s also good to find out more about email bounce back and the reasons so that it could be resolved.