Are you receiving an error code on your screen after sending an email? Don’t know the reason behind this error code?

Don’t worry as these codes are the Gmail errors occurring due to the failure of the delivery of the email you sent.

According to a Statista report, the number of emails sent per day in 2026 will reach 392.5 billion.

Some emails are not able to pass the authentication check. The issues in the email delivery can range from incorrect email credentials to issues in the receiver’s domain. Hence, after the failure to deliver emails, an error code is generated.

Every error code has a specific message. This error message explains the reason behind the failure.

Here is a detailed guide on Gmail error codes, what each error code means, and how to resolve the issue.

What are Gmail Error codes?

Gmail error codes are generated when the email server is unable to deliver the email. It appears as a result of the failure of email delivery. Email error codes are also referred to as SMTP error codes or bounce codes.

The error codes appear with the error messages, explaining the reason behind the failure. The three-digit code includes the representation of the error generated from the server. And the message portion explains the reason behind failure.

Why are the error codes important to know?

For domains sending large amounts of emails, understanding error codes is essential. These codes tell a domain what went wrong and how to fix the issue.

All email providers have a list of error codes with their explanations. Like other MSPs, Google also has a detailed guide on the error codes and their meanings.

These Gmail codes must be known to help resolve email delivery issues quickly. These codes can save time and improve the functioning of the domain. Domain owners can use the saved time to fix the issue.

How to Read Codes?

The Gmail error codes are divided into categories from 200 – 600. It is a three-digit code that appears with a message. One must know the meaning of the categories to understand if the error is temporary or permanent.

Codes in the range 200-299

The codes starting from 2 indicate that the email has been delivered. This may have been labeled as an error code. But it works as a confirmation message. Any code in this range indicates the Delivery Status Notification’s report on successful delivery. Hence, there are no issues in the email delivery.

Codes from 400-499

Error codes in the range of 400 to 499 depict a delay in the email delivery. It shows that there is a temporary failure of the email delivery. These codes appear in non-delivery reports. It shows that the email will be re-sent later. The failed email has the potential to be delivered later.

Codes from 500-599

Codes in this range mean the permanent failure of email delivery. The original email couldn’t be delivered due to issues with the sender’s or receiver’s domain. It needs an adjustment for delivery.

If the code from this range appears, the MTA server removes the message and sends a non-delivery response to the sender. The sender can then try ending another email with the adjustments.

Error Codes and Their Solutions

Here are the most common error codes, the reasons behind them, and their possible solutions.

Error Code 421 (4.7.0)

Error code 421 is divided into three categories

• The connection has expired. Reconnect and send the email again.
• The IP address sending the email is not on the whitelist (not approved) from the recipient’s domain. Therefore the email was unable to be delivered.
• The recipient’s domain doesn’t support a TLS connection. Therefore, email is unable to be delivered to that domain.

Possible Solution: 

Check your network connection. Make the Google SMTP settings accurate. If the issue still persists, visit the Gmail Help Center.

Error Code 450 (4.2.1)

Error code 450 is divided into three categories

• The receiver is receiving mail quickly and is unable to receive your mail. You can try when the receiver’s inbox becomes available. Your email might be delivered then.
• The receiver’s inbox is not accepting additional emails. The sender must wait and try sending the mail again. This is a temporary issue.
• The receiver’s SMTP relay limit is crossed. It can occur if the server on the receiver’s side is not accepting Non-deliverable responses. To learn more about the SMTP relay limit, review SMTP relay service error messages.

Possible Solution: 

To resolve error 4.2.1, the wait is the best solution. Resend the email after the recipient’s domain gets lighter.

Error Code 451

• 4.3.0: The sender’s server doesn’t allow sending emails to multiple domains in one go.
• 4.4.2: The sending time limit is exceeded. The connection is thereby closed.
• 4.5.0: The email has violated the SMTP protocol. Hence, it can not be sent.
• 4.7.23: The IP address of the sender doesn’t have the PTR record.
• 4.7.24: The SPF record of the sender’s domain recorded any suspicious activity. Therefore, emails from the sender’s IP address have been temporarily blocked.

Possible Solution: 

It is essential to learn about the email sending limit of your domain. Review the security settings on your domain and verify the Gmail server status.

Error Code 550

• 5.1.1: You are entering the wrong receiver’s email address. Check it for mistakes and resend again.
• 5.2.1: The email account is not active right now. Try again when they activate their account.
• 5.2.1: The receiver’s domain is not accepting additional emails.
• 5.4.5: The user’s SMTP relay limit is crossed. To get an idea about the SMTP relay limit, review SMTP relay service error messages.
• 5.5.3: The sender’s server doesn’t support sending emails to more than one recipient.
• 5.7.26: It means the mail has been blocked because the sender is unauthenticated.

Possible Solution: 

Recheck the recipient’s email address. Check if your email address and the recipient’s email address are in the whitelist. Do a thorough malware check.

Error Code 552

• 5.2.2: The receiver’s inbox doesn’t have enough storage to receive the email.
• 5.3.4: The sent email crossed the size limit issued by Google. It could be the size of the message header or the size of a single header value.
• 5.7.0: The email’s content didn’t go with the security rules and presented a threat. Therefore, it was blocked to prevent the recipient’s inbox from scams.

Possible Solution: 

The recipient must make space in their inbox. Fix the email size if it is exceeding the limit. If the issue persists, confirm if the email address is active and is not blacklisted.

Error Code 553 (5.5.1)

The command has failed to proceed as the mailbox name doesn’t exist. It can appear due to:

• The DATA command can’t be used after the BDAT command.
• The MAIL transaction protocol is being used after giving the command.
• The RCPT mail transaction protocol has been issued out of sequence.

Possible Solution: 

Re-check the recipient’s email address. Check any existing typos and make sure you are sending the email to the active domain.

You can learn more about the Gmail error codes and their explanation here.

Conclusion

In short, Gmail uses error codes to display the issues in the email delivery. These error codes serve to inform the senders about the issues on their domain. Some Gmail error codes also signal email authentication issues.

Proper implementation of DMARC and authentication protocols can protect the domains from failures. You can also get help from PowerDMARC to strengthen your email’s security.