Sudden failure to send emails through specified SMTP server with python script

Anonymous
2021-07-15T20:57:04+00:00

Hi,

We have been sending automated emails through a python script for a while now and suddenly getting this error:

Failed to send an E-mail through the specified SMTP server [smtp.office365.com]:
Mailbox unavailable. The server response was: 5.2.252 Sender throttled due to continuous send as denied errors.
[Hostname=BN9PR12MB5179.namprd12.prod.outlook.com]

All of the login/password information is correct in the python script for sending the email, so why is this suddenly happening?

Microsoft 365 and Office | Subscription, account, billing | For business | Other

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  1. Anonymous
    2021-07-22T10:07:01+00:00

    We have been having this issue all week.

    On our UK customer sites, our Service application that has been running flawlessly for months now times out when sending via SMTP. Restarting the service temporarily fixes the issue but it reoccurs a few times every day. This is only affecting Office 365 SMTP servers.

    For us, login fails with a 535 error.

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  2. Anonymous
    2021-07-22T13:44:05+00:00

    This is causing major issues and Microsoft won't get back to us. Can you please resolve this? I spent hours and hours looking at this for a few days before I saw this thread.

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  3. Anonymous
    2021-07-22T14:03:31+00:00

    Some good news here. For the first time in the past week, we don't have the error message when sending out email from applications. I am not sure if this is because MS fixed the issue or we haven't reach the threshold yet. I will keep monitoring this and report back here.

    Can someone please verify if this got fixed for you as well?

    Thanks

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  4. Anonymous
    2021-07-22T14:22:21+00:00

    I can verify that we have not had this error crop up again since Tuesday after switching our license for our sending account. I don't feel confident that was really a fix but probably more of a reset. But maybe Microsoft has changed something so it won't error out again? I wish I had more information.

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  5. Anonymous
    2021-07-22T14:28:52+00:00

    I can verify that we are not having the issue anymore as well. Nothing was changed other than calling microsoft multiple times to complain and get help with it.

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