Resolve an email issue (following an error report)

This guide helps you identify and correct most email errors encountered after sending an email to a recipient.

Why an Email Error?

Generally, an email error message results from:

• a misconfiguration of the domain name used with your email service
• a problem with your recipient's (mail provider)

In any case, a delivery failure report (Mailer Daemon or Mail Delivery Subsystem) containing the explanation is sent to the sender.

Finding and Identifying the Email Error

When your message fails to reach your recipient, an initial failure report (Temporary Delivery Failure Report) is sent and specifies that the server will attempt to resend your message multiple times.

A final non-delivery report (Final Delivery Failure Report or Undeliverable Mail) issued by the recipient's server is sent to the sender (via an Infomaniak mail server, hence the mention of Infomaniak at the beginning of most error messages you may receive) to inform them that the email could not be delivered even after multiple attempts.

The notification always includes the reason for the failure. Example below:

This is the mail system at host smtp-1-1234.mail.infomaniak.ch.
I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can delete your own text from the attached returned message.
The mail system anna.a@abc.xyz: host mxbw-abc-xyz.abc-ab12.abc.ch[123.456.789.00] said: 550 5.1.1
anna.a@abc.xyz recipient rejected, account administratively disabled (in reply to RCPT TO command) 

Here, the recipient's address is apparently suspended by their email provider (account administratively disabled).

Sometimes, you need to look for the reason for the error message among its attachments (often a plain text file). Example:

Reporting-MTA: dns; mxbw.abc.ch‍ [123.456.789.00]
Received-From-MTA: dns; smtp-1-1234.mail.infomaniak.ch [12.345.678.99]
Arrival-Date: Tue, 01 Aug 2023 15:49:22 +0200
Final-recipient: rfc822; anna.a@abc.xyz
Diagnostic-Code: smtp; 552 RCPT TO:anna.a@abc.xyz‍ Mailbox disk quota exceeded
Last-attempt-Date: Tue, 01 Aug 2023 15:49:22 +0200

Here, the external recipient's mailbox at Infomaniak appears to be full (Mailbox disk quota exceeded).

Most Common Cases

SPF Failure

The SPF (Sender Policy Framework) record is not properly configured:

Subject: Delivery Status Notification (Failure)
From: Mail Delivery System mailer-daemon@domain.xyz
To: Anna.A anna.a@abc.xyz
This is an automatically generated Delivery Status Notification.
Delivery to the following recipient failed due to SPF failure:
anna.a@abc.xyz
Technical details of SPF failure:
The sender's domain domain.xyz does not have a valid SPF record. Please contact your email administrator to correct the SPF configuration.

Solution: check your domain name configuration and especially the SPF record if your website is hosted by Wix or another provider. Learn more (click here)

User Unknown

The email address specified in the message is invalid or does not exist:

Subject: Delivery Status Notification (Failure)
From: Mail Delivery System mailer-daemon@domain.xyz
To: Anna.A anna.a@abc.xyz
This is an automatically generated Delivery Status Notification.
Delivery to the following recipient failed permanently:
anna.a@abc.xyz
Technical details of permanent failure:
The email address does not exist. Please check the recipient's email address and try again.

Solution: carefully check the recipient's email address and correct it if necessary; ensure you are using a valid email address for the recipient.

Temporary Failure

The recipient's mail server is experiencing temporary issues or is unavailable.

Solution: wait for some time, then try sending the message again later. If the problem persists, contact the recipient's technical support for assistance.

Blocked by SPAM Filter (or Content Rejected)

The recipient's mail server blocked the message due to anti-spam filtering rules:

Subject: Delivery Status Notification (Failure)
From: Mail Delivery System mailer-daemon@domain.xyz
To: Anna.A anna.a@domain.xyz
This is an automatically generated Delivery Status Notification.
Delivery to the following recipient failed due to the message being rejected as spam:
anna.a@domain.xyz
Technical details of delivery failure:
The content of the message triggered the spam filters of the recipient's email server. Please review the message content and try again.

Solution: check if your message contains elements likely to be considered as spam (keywords, suspicious links, etc.). Contact the recipient to verify if the message was filtered into the spam folder.

Read this guide on outgoing spam and this guide on incoming spam.

Bad Reputation

The recipient's mail server blocked the message due to anti-spam filtering rules:

gmail-smtp-in.l.google.com said: 550-5.7.1
Our system has detected that this message is likely suspicious due to the very low reputation of the sending domain.
To best protect our users from spam, the message has been blocked.
Please visit https://support.google.com/mail/answer/188131 for more information.

Solution: check the reputation of the domain, determine if there has been recent misuse of one of your email addresses for malicious purposes, e.g.

Domain Not Found (or DNS Error)

The recipient's domain name could not be resolved or does not exist.

Solution: check the spelling of the recipient's domain and correct it if necessary; ensure that the domain name and DNS are valid and active.

Mailbox Full

The recipient's mailbox is full, preventing the reception of new messages.

Solution: inform the recipient of the situation and ask them to free up space by deleting emails or archiving items.

This cannot happen with email addresses managed by Infomaniak since they do not have a storage size limit.

Part of their network is on our block list

If the error message (typically obtained after sending from an online tool hosted on the server where your website is located, e.g., a confirmation from Prestashop or another online store you manage) contains:

host hotmail-com.olc.protection.outlook.com[104.47.30.97] said: 550 5.7.1
Unfortunately, messages from [89.123.456.789] weren't sent. Please contact your Internet service provider since part of their network is on our block list.

Solution: change the method of sending emails. The sending is unauthenticated and comes from a specific IP address which is apparently blocked by the recipient for some reason (Infomaniak does not intervene to request unblocking). Therefore, configure the online tool to perform authenticated sends.

Less Common Errors

Deferred - Delayed

The error message Deferred - Delayed - Warning: message still undelivered after 4 hours, Will keep trying until message is 3 days old means that the Infomaniak mail server tried to connect to your recipient's mail server to send the message but for some unknown reason, it was unsuccessful. This error message specifies that the Infomaniak server will continue to try to send your message for the period specified in the error message. If after this period the message is still not delivered, you will receive a final error message informing you that your message could not be delivered and your recipient did not receive it.

Greylisting Delay

This Greylisting Delay error occurs when your recipient's mail server uses, like Infomaniak, a technique called "greylisting" which imposes a temporary delay on the first attempt to deliver a message from an unknown sender. The Mailer Daemon may eventually send an error report indicating that delivery has been delayed due to greylisting. The error may also mention banned sender. Retry your sending a few minutes/hours later.

Message Size Exceeded / File Too Large

These Message Size Exceeded / File Too Large errors occur when the size of the message (or attachments) exceeds the limit allowed by the recipient's mail server. The Mailer Daemon will return an error report indicating that delivery failed due to exceeding the message size.

Rate Limit Exceeded

This Rate Limit Exceeded error occurs when the sender has exceeded the rate or volume limit allowed by the recipient's mail server. Mail servers may impose limits to prevent spam or system overload.

Malware Message Rejected

This Malware Message Rejected error occurs when the message contains an attachment, a link to a storage site like Dropbox, or dynamic content including in the "forwarded" part of the message (e.g., in a forwarded message). Try resending the message from Infomaniak Mail instead of a mail application, and remove any content that could trigger this error.

The Message Contains a Unicode Character in a Disallowed Header

This The message contains a unicode character in a disallowed header error may appear if you have inserted a special character like a heart ♥ e.g., in the body of the mail, the subject, or especially in the full name; the risk of being rejected by providers is very high: keep the use of symbols, characters, and fonts as simple as possible.