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I have a question. When i send email with my emailbox, it's ok. But my customer send email, it alert :Authentication unsuccessful! by the way ,he send eamil is also OK by outlook with the same email account. can you tell me why?


Mail.dll: 10 11:12:59 C: AUTH LOGIN
Mail.dll: 10 11:12:59 S: 334 VXNlcm5hbWU6
Mail.dll: 10 11:12:59 C: dGVzdDFAYmpqaS1jdXR0aW5ndG9vbHMuY29t
Mail.dll: 10 11:12:59 S: 334 UGFzc3dvcmQ6
Mail.dll: 10 11:12:59 C: XYZ (removed for safety)
Mail.dll: 10 11:12:59 S: 535 5.7.3 Authentication unsuccessful

I don't think this is a server side problem, because this email account can send email normally ‍by Microsoft outlook or other third party email program.

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The error is clear: Authentication unsuccessful. Please check your credentials, or consult your SMTP server administrator.

The user name you are using to log-in to the server is:

Have you tried dropping the domain part and using "yuanjie" only?

by (298k points)
It turned out that skipping the domain part was the solution!