Relay smtp.office365.com

Question

Hello all

I have a server that is failing to relay through smtp.office365.com on port 587. Below is the error i am receiving . I have verified that the username and password are correct. When i look at the azure sign-in log files it is showing that the account is able to log in successfully for SMTP, however the error below is suggesting that the account is failing to log in. Any help in is greatly appreciated

"The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.57 Client not authenticated to send mail. Error: 535 5.7.3 Authentication unsuccessful [TYWPR01CA0028.jpnprd01.prod.outlook.com]"

Answer 1

Hi @Skip Hofmann

Here is a link about the several possible cause of this issue: Error: Authentication unsuccessful
Please also have a check if the security default is enabled in the tenant.

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Answer 2

Is SMTP client submission enabled for the account? Check via:

Get-CASMailbox mailboxname | select SmtpClientAuthenticationDisabled

and make sure to also check the tenant-wide setting:

Get-TransportConfig | select SmtpClientAuthenticationDisabled