When an email is refused by the SMTP service, it means the message was not accepted by the server and was not forwarded for delivery. This article presents the most common causes and the actions to take to resolve the issue.
What it's used for
Identifying the reason for a refusal allows you to:
- Quickly correct the problem and resend the message
- Prevent the same situation from happening again
- Understand which error code corresponds to which cause
Common causes of a refusal
Unauthenticated sender domain
The domain used in the sender address is not properly validated in your SMTP account. Verify that your 3 CNAME records (DKIM 1, DKIM 2, and SPF/Return-Path (MX)) are properly configured and validated in the Domains tab.
Sender domain does not match your SMTP user
Each SMTP user is linked to a specific domain. If the sender address configured in your application does not belong to the same domain as the SMTP user used for sending, the message will be refused. Verify that the domain of your From address (e.g., your-company.com) matches the domain associated with your SMTP user in the Domains tab.
Sending quota reached
The monthly limit of your plan has been reached. New messages are refused until the billing period renews or a higher plan is selected in the Pricing tab.
Too many recipients
A message can contain a maximum of 50 recipients. Recipients beyond this limit are refused. If you need to reach more people, split the mailing into multiple messages.
Message too large
The total size of the message, attachments included, exceeds 20 MB. Reduce the size of attachments to stay within this limit.
Unauthorized or invalid attachment
Some file types are not accepted by the service. A message may also be refused if the content of an attachment does not match its extension (e.g., a file renamed to .pdf that is not actually a PDF). Make sure your attachments use a common file format and that their content matches their extension.
Learn more >
Invalid address
The sender or recipient address is incorrectly formatted or does not exist. Verify that all addresses used are correctly entered.
What to do if my message is refused
- Hover over the Rejected status label in the Activity tab to display the reason for the issue directly in the list. This is often the fastest way to identify the cause.
- Check the error code displayed by your application — refer to the article SMTP error codes: what they mean to identify the precise cause.
- Verify that your domain is properly authenticated in the Domains tab. The three records DKIM 1, DKIM 2, and SPF/Return-Path (MX) must all display a Valid status (green circle).
- Check your sending quota in the Dashboard.
- Verify that the message respects the limits: 50 recipients maximum, 20 MB maximum.
- Check your SMTP credentials in your application's configuration.
If the problem persists, note the exact error code and contact our support team.
See also