Understand the main email (SMTP) error codes and what to do about them

Procédure

Objective

When sending an e-mail fails, you often receive a return message containing an SMTP error code.
This guide will help you to understand the most common error codes, identify the cause of the problem and find out what checks to carry out to try and resolve the situation.

Concerns

• Customers withpersonalised emails associated with a domain name or LWS hosting
• Use via :
  • Webmail
  • Email software (Outlook, Thunderbird, Apple Mail, etc.)
  • Script or website sending emails

Requirements

Before using this guide, please make sure you have the following information:

• The complete error message received after the sending failure
• The SMTP code in the message (e.g. 550 5.1.1)
• The e-mail address of the recipient concerned

This information can generally be found in the automatic return message (called a "bounce") received after your email was sent.

How to use this guide

1. Locate the SMTP error code in the bounce message.
2. Look for this code in the list below.
3. See :
   - what the error means.
   - possible causes
   - what to check.

SMTP 550 error 5.1.1: destination e-mail address does not exist

What this error means

The email server indicates that the recipient's email address does not exist.

Possible causes

• The e-mail address has been misspelled.
• The address has been deleted.
• A list of recipients contains invalid addresses.

Example of an error message

You may receive a message similar to :

SMTP error 550 5.1.1User unknown No such user here This user doesn't have a XXX account Message rejected (no valid recipients) Invalid recipient User not found Sorry, no mailbox here by that name ... is not a valid mailbox Requested action not taken: mailbox unavailable Recipient address rejected : User unknown in local recipient table The email account that you tried to reach does not exist I'm sorry to have to inform you that the message returned below could not be delivered to one or more destinations A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed Unable to deliver message to the following address(es) Delivery to the following recipients failed permanently

What should I do?

1. Check the recipient's e-mail address.
2. Make sure that the part before the @ is written correctly.
3. If you are sending an e-mail to several recipients: test the delivery with a single address.
4. If the address comes from a contact list: check that the list is up to date.

Check

Repeat the send test after correcting the address.
If the email is accepted by the server without an error message, the problem has been solved.

SMTP 550 5.2.1 error: recipient email address disabled

What this error means

The email address exists, but it has been deactivated by the recipient's email provider.

Example message

Mailbox disabled Not accepting messages Mailbox disabled

This can happen, for example, if :

• The account is inactive.
• The account has been suspended.
• The provider is temporarily blocking the box.

What should I do?

In this case, you cannot correct the problem yourself.

Possible solutions:

• contact your correspondent by another means
• wait for the supplier to reactivate the box.

SMTP error 544 5.4.4: destination domain name not found

What this error means

The recipient domain name (part after the @) does not exist or is not correctly configured.

Example: contact@exemple-domaine-inexistant.com

Examples of error messages

Host not found Host unknown Recipient address rejected : Domain not found

Possible causes

• typing error in the domain
• domain expired
• Domain not configured to receive email

What should I do?

1. Check the part after the @ in the email address.
2. Correct any typing errors.
3. Contact your correspondent if necessary to confirm the correct address.

SMTP error 552 5.3.4: e-mail too large

Message size exceeds fixed maximum message size

SMTP error 452 4.2.2 or 552 4.2.2: recipient's mailbox full

Disc quota exceeded Over quota Mailbox full

SMTP error 451 4.4.1 or 451 4.4.2: the recipient's mail service is not responding

What this error means

The recipient's mail server is temporarily not responding.

Example of an error message

This is a warning message only. You do not need to resend your message Warning: Cannot send message for past X hours

This may be caused by :

• server overload
• maintenance
• a temporary network problem

What happens in this case

Your email server may automatically retry sending for a while.

What should you do?

In most cases :

1. Wait a few hours.
2. Let the system retry sending automatically.

If the problem persists for several hours or days, contact the recipient to check that their email service is working correctly.

SMTP error 450 4.1.8: your email address is wrong

What this error means

The server indicates that the e-mail address used as the sender is incorrect.

Example of error message

Sender address rejected: Domain not found

Possible causes

• Incorrect configuration of your e-mail address.
• Error in the sending parameters

What should you do?

1. Check the address used as the sender.
2. Check the configuration of your e-mail software.
3. Make sure you are using the correct SMTP settings.

SMTP error 550 or 554: permission problem, blocking or spam filtering

What this error means

SMTP 550 or 554 errors can occur when the recipient's mail server refuses to receive your message.

Despite LWS's efforts to maintain a good reputation for its mail servers, in particular through the fight against spam, it can happen that some mail providers temporarily block a sending server.

In this case, your message may be refused by the recipient's server.

Example of an error message

Permission denied Connection refused Mail rejected by Windows Live Hotmail for policy reasons. The mail server IP connecting to Windows Live Hotmail has exhibited namespace mining behavior Delivery temporarily suspended Messages from xxxxx temporarily deferred due to user complaints Mail rejected by Windows Live Hotmail for policy reasons. Reasons for rejection may be related to content with spam-like characteristics or IP/domain reputation problems. Unfortunately, messages from [xxx.xxx.xxx.xxx] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140) Spam detected Too many errors from your IP

Possible causes

There are several possible reasons for this block:

• The message looks like spam.
• TheIP address of the sending server is temporarily blocked.
• The content of the message is considered suspicious.
• Too many errors or mailings have been detected from the server.
• User complaints have been reported to the recipient's email provider.

In these situations, the decision to block is taken by the recipient's server, not by LWS.

What can I do to resolve the problem?

- If the message indicates a temporary block.

Some messages indicate that the refusal is temporary.

In this case :

1. Wait a few hours.
2. Then try sending your e-mail again.

The problem is often resolved automatically.

- If the message is identified as spam.

If your email has been detected as potential spam, try to :

• modify the content of the message
• avoid words or phrases often used in spam
• reduce the number of links or images
• avoid unusual attachments

Email providers use different anti-spam systems, the rules of which are not public.

For this reason, LWS support does not have precise information on their anti-spam filters.

Check that the problem has been solved

After applying the solution corresponding to your error :

1. Send a test e-mail.
2. Check whether you receive a new error message.
3. If no error message appears, the e-mail is being sent correctly.

If the problem persists

If the error continues to appear :

1. Keep the complete error message.
2. Make a note of: the recipient's address and the date and time of sending.
3. Contact technical support with this information.

Best practices for avoiding email errors

To reduce the number of errors when sending emails:

• Always check the spelling of email addresses.
• Avoid sending attachments that are too large.
• Keep your contact lists up to date
• Test your mailings before sending to several recipients.

Conclusion

SMTP error codes can be used to identify the cause of an email sending problem and to guide the checks to be carried out. If in doubt, or if the error persists, don't hesitate to contact technical support with the full error message.