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
    2021-07-20T19:55:05+00:00

    Seems to be working for us now but can't figure out a way to resend the bounced email in the badmail queue on our smtp server. So have to manually resend about 100 from our system. What a pain..

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  2. Anonymous
    2021-07-20T20:20:24+00:00

    Same problem here for my application that sends emails to multiple accounts up to 20 accounts get notified but now the application debugs to this error:

    5.2.252 Sender throttled due to continuous send as denied errors.

    my developers were using a manual list which got out dated and there were a few bounce backs for users that left the company about a year ago.

    so we cleaned up this list already and will go with distribution lists going forward but in the mean time still get this error: 5.2.252 Sender throttled due to continuous send as denied errors.

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  3. Anonymous
    2021-07-20T20:25:09+00:00

    We started having this same issue this morning. We use a SMTP server and it has blocked the account we use to email all of our business graphs and reports. Totally locked up now and have no way to unlock. Deleted 4,600+ emails in the Queue.

    Ticket opened up with Microsoft. Waiting...........

    07-21-2021 Update

    Spoke with MS for about 20 min yesterday and they got it running again. However the problem came right back this morning. Have reopened ticket with them to see what is going on.......

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  4. Anonymous
    2021-07-20T20:35:08+00:00

    Unfortunately, my issue came back.

    Mailbox unavailable. The server response was: 5.2.252 Sender throttled due to continuous send as denied errors.

    [Hostname=DM6PR12MB4793.namprd12.prod.outlook.com]

    I noticed that for the two mailboxes that have the issue, there are a lot of "SendAs" events, which is baffling because I am using the owner to send out the email, there is no "SendAS" required.

    For the mailbox which doesn't have the issue, I don't find any "SendAs" event.

    I have updated the MS tech, hopefully, they will come out of some permanent fix soon for everyone.

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    1 person found this answer helpful.
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  5. Anonymous
    2021-07-20T22:22:00+00:00

    Let us know what the tech says, this is still happening for us. Even with a newly created email address.

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