How to resolve the "526 Authentication failure" bounce message-Alibaba Mail(Alibaba Mail)-阿里云帮助中心

Problem

When you send an email from a third-party client or programmatically, the operation fails and returns a bounce message with the following information:

526 Authentication failure

Cause

This error occurs because Alibaba Mail requires account authentication when you send emails from a third-party client or programmatically.

Solution

Incorrect username: Verify that the SMTP authentication username is correct. This username must be your full email address and must not contain extra characters, such as spaces.
- For example, a***@example.net.
Incorrect SMTP password:
- If you have not enabled the security password for third-party clients, use your email account's login password. The password must not contain extra characters, such as spaces.
- If you have enabled the security password for third-party clients, you must use the generated password to log in. For more information, see Enable and set a security password for third-party clients.
Incorrect server address:
- Verify that the SMTP server address is correct. For more information, see IMAP, POP, and SMTP server addresses and port configurations.
Access policy restrictions:
- Verify that the SMTP protocol is enabled. For more information, see Configure access control and security policies for third-party clients.
- Verify that the scope of the access policy includes the sender's email address and that no login restrictions exist based on IP address or client type.
- Verify that the request frequency does not exceed the limit. The recommended limit is 10 requests per second.