How to Solve the Prompt "526Authenticationfailure" for Returning Letters - Alibaba Mail

Problem Description

Failed to send the email by Alibaba Mail, and the returned email contains the following information:

526 Authentication failure

When the Alibaba Mail uses a local email client or code to send emails, the account needs to be authenticated.

Incorrect account name: Please enter the SMTP authentication login user name (complete email address) correctly and do not contain extra characters such as spaces.
- For example, a***@example.net.
Incorrect SMTP password:
- Use the logon password of your account. Please do not enter extra characters such as spaces. f
Incorrect server address:
- Set the specified email sending server. The default sending email server address is smtp.sg.aliyun.com and the port is 25 (encryption port is 465). For more information, please check IMAP, POP and SMTP Server and Port Information of Alibaba Mail.