The SMTP server requires a secure connection or the client was not authenticated

Question

Hi All

i am using exchange 2016 hybrid environment. I am using the below syntax. i am getting the error. experts guide me
when prompted for credentials i am giving service account svc@Company portal .com. this service account is created as remote mailbox in exchange onprem and it has exchange online license.
ug@Company portal .com is a unified group and svc@Company portal .com has send as permissions on ug@Company portal .com. there is no issue with the credentials.

Send-MailMessage -SmtpServer smtp.office365.com -Credential $credential -From '******@contoso.com' -To '******@contoso.com' -Subject 'TEST' -Port 587 -UseSsl  

Error: 535 5.7.139 Authentication unsuccessful, the user credentials were incorrect.
[JIKPIOP.PROD.OUTLOOK.COM]
At line:1 char:1

• Send-MailMessage -SmtpServer smtp.office365.com -Credential $credenti ...
• ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
• CategoryInfo : InvalidOperation: (System.Net.Mail.SmtpClient:SmtpClient) [Send-MailMessage], SmtpException
• FullyQualifiedErrorId : SmtpException,Microsoft.PowerShell.Commands.SendMailMessage

Answer 1

Hi @Glenn Maxwell

Thank you for asking this question on the **Microsoft Q&A Platform. **

Check if the user has the MFA active, in that case, you must deactivate the MFA for that user,

I cannot use MFA to send emails via PowerShell.

Hope this helps,
Carlos Solís Salazar

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Answer 2

Hi @Glenn Maxwell

If SMTP auth isn't enabled in your tenant or for this service account (svc@Company portal .com), you would also receive this error: 535 5.7.139 Authentication unsuccessful, the user credentials were incorrect.
Please refer to this link: Error: Authentication unsuccessful

The most common cause may be security defaults is enabled in your tenant. If yes, you may need to disable it first to use SMTP auth.
If this is not the cause, please also check the other possible causes in the link.
For example, make sure SMTP auth is enabled for the service account, make sure MFA is disabled.

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