535 5.7.139 Authentication unsuccessful

Question

We are receiving the following error using the Office 365 SMTP server to send mails:

535 5.7.139 Authentication unsuccessful, the request did not meet the criteria to be authenticated successfully.

Same issue with MFA (+ App password) and without MFA. Authenticated SMTP is activated for the used account. Unfortunately the provided error message is a bit vague.

Request options:

host: 'smtp.office365.com',
port: 587,
auth: {
user: USER,
pass: PASS
}

optional additional tries included specific TLS config (requireTLS: true, tls: { ciphers: 'SSLv3' }) which also resulted in the same error message.

Authentication data is correct as changing them shows a different authentication error (535 5.7.139 Authentication unsuccessful, the user credentials were incorrect).

Using the given domain XXXX.mail.protection.outlook.com (port 25) is not constant as some IPs are blacklisted so this is not an option.

Any information what this error means and what it causes would be appreciated since we can only find recent unanswered information about this error.

Thanks in advance

Answer 1

Hi @Maurice Wegner

To my knowledge, there may be other two possible causes of this issue.
Please refer to this link and check point 3 (Azure Security Defaults) and point 4 (Conditional Access policy): Error: Authentication unsuccessful

These settings would block Legacy Authentication.

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Answer 2

We got this error when we set up a Lexmark X736de MFP network scanner/printer

the way to setup the printer is nicely explained here:

The user account used for authentification needs to have a licenced exchange subscription so shared mailboxes do not work

Azure Security Defaults are set to "NO"
No conditional access policies are active but the selected user uses MFA Multifactor authentifaction anyway.

When trying to scan we got errors like "535 5.7.139 authentication unsuccessful"

You can check in azure acive directory --> users --> user that you want to authenticate --> sign-in logs for details

As a work around you can use an APP PASSWORD which can be created by

• login into the relevant o365 user account --> clicking on user icon in upper right corner on browser (office account, not brower profile) -> view account --> my sign-ins --> security info --> add method --> app password

When setting up the smtp user account of the printer use the email address + app password (instead of the normal user password connected to MFA)

Answer 3

I know this is an old message but it is a top search result and maybe this helps someone.

To get SMTP Auth to work I had to exclude the account from all four of the "baseline" Conditional Access policies EVEN INCLUDING the two that are for tenant admins and Azure admins, which it isn't.  Otherwise 365 rejects the connection with message, "Authentication unsuccessful, the request did not meet the criteria to be authenticated successfully." I found this because I tried to log in to maybe create an app password and it was still prompting me to set up MFA.

Each user (or the tenant) also has to have SMTP Authentication enabled.

Answer 4

It might be best to use Direct Send in this scenario. Nevertheless, my blog post explains what you need to know to resolve this error: https://ourcloudnetwork.com/how-to-fix-error-535-5-7-139-authentication-unsuccessful/