535: 5.7.3 Authentication unsuccessful

Anonymous
2020-04-16T10:47:36+00:00

Hello,

I have an issue when using an O365 account and sending emails from an application.

The application has been suitable to use tls/starttls, port 587, ect.

When entering an email account and password, the following message occurs:

"535: 5.7.3 Authentication unsuccessful"

I would like to understand, what are the mininal features of an O365 account so that it can be used from another application.

I have performed different tests, which allow me to indicate that the account is Ok.

Thank you.

Microsoft 365 and Office | Subscription, account, billing | For home | Windows

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  1. Anonymous
    2020-06-23T20:50:15+00:00

    I tried this. I was using smtp.office365.com and port 587. However I switched to [domain].mail.protection.outlook.com and port 25 as advised and now I see this error:

    The SMTP server does not support authentication.

    This seesm to have occurred after I enabled "secure defaults" in Azure AD. I have enabled SMTP Authentication for the domain user's mail box who I am attempting to authenticate with.

    Do I need to also turn SMTP auth on at the organisation / tenant level?

    Update: it looks like this person encountered the same issue and found a solution: 

    https://community.spiceworks.com/topic/2276644-everything-using-office-365-smtp-authentication-is-broken-wont-authenticate

    I'll create a seperate answer.

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  2. Anonymous
    2020-06-23T19:15:16+00:00

    Same issue here, also in UK.

    This was working fine for us until we enabled "Secure Defaults" in Azure Active Directory. We then came back and enabled the "Authenticated SMTP" setting against the mailbox, but it is currently still failing. I am hoping the settings update just takes a while to propagate but the docs do not make that clear.

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  3. Anonymous
    2020-06-10T10:32:20+00:00

    Hi Everyone,

    I managed to fix the problem, my problem was that in the software the credential information took it from another site, had to make a adjustment in the development. Then it worked.

    I do not have the detail of the O365 configuration, I am not the administrator

    Thank you very much!

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  4. Anonymous
    2020-06-10T09:36:28+00:00

    I have an almost identical problem. 

    Telnet:

    open smtp.office365.com 587

    Output:

    220 LO2P265CA0199.outlook.office365.com Microsoft ESMTP MAIL Service ready at Wed, 10 Jun 2020 09:31:18 +0000

    Telnet:

    EHLO

    Output:

    250-LO2P265CA0199.outlook.office365.com Hello [XX.XX.XX.XX]

    250-SIZE 157286400

    250-PIPELINING

    250-DSN

    250-ENHANCEDSTATUSCODES

    250-STARTTLS

    250-8BITMIME

    250-BINARYMIME

    250-CHUNKING

    250 SMTPUTF8

    Telnet:

    AUTH LOGIN

    Output:

    504 5.7.4 Unrecognized authentication type [LO2P265CA0199.GBRP265.PROD.OUTLOOK.COM]

    When I try from a completely different IP network using a different OS and different email package, I get:

    535 5.7.3 Authentication unsuccessful [LO2P265CA0199.GBRP265.PROD.OUTLOOK.COM]

    UK based if that helps.

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  5. Anonymous
    2020-06-02T19:00:30+00:00

    My team is also recieveing this issue, and we also have enabled Authenticated SMTP.

    This was working for us two weeks ago, so I think something was just broken behind the scenes.

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