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?

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  1. Anonymous
    2021-07-16T08:20:52+00:00

    Hi ahesse47

    Greetings

    Thank you for posting in Microsoft Community.

    To help me better assist you kindly verify how you're accessing your outlook, is it via outlook on the web or outlook desktop client.

    You can try to perform the following steps to help resolve the issue:

    1. Check the Network Settings. Check you internet connection and make sure that the system is connected to a working network.
    2. Check the Account Settings. Check your Outlook account settings to ensure there is no indecent setting causing you to experience this error.
    3. Configure Firewall. It may be possible that your Windows Firewall program is blocking your Outlook application for safety issues. Configure Firewall and allow Outlook to use the internet connection.
    4. lastly try to send mail using a different environment or browser and check to see if the same error appears.

    Please feel free to let me know how it goes

    Regards,

    Momo

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  2. Anonymous
    2021-07-19T07:35:14+00:00

    Hi ahesse47

    I'm following up on this thread, any update?

    Thanks,

    Momo

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  3. Anonymous
    2021-07-19T13:36:27+00:00

    I have checked all of the settings you recommended above and none of them are the issue. When trying to send any email via SMTP it still gives the same error:

    Sender throttled due to continuous send as denied errors.
    [Hostname=BN9PR12MB5179.namprd12.prod.outlook.com]

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  4. Anonymous
    2021-07-20T10:39:44+00:00

    Am Seeing the same issue. By any chance are you using IIS SMTP server to replay messages?

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  5. Anonymous
    2021-07-20T13:14:24+00:00

    We are facing the same issue. Couple of mailboxes we are using for the scan to Email or notification from D365, start to get this error after sending out some emails. When this happens, we have to wait for hours, then it starts to work for a couple of hours.

    Here is the error message:" Mailbox unavailable. The server response was: 5.2.252 Sender throttled due to continuous send as 

    denied errors. [Hostname=BL0PR12MB5012.namprd12.prod.outlook.com]

    Looks like there is some mechanism in o365 to throttle those emails. I have opened a support ticket with MS, but no luck yet.

    Any help?

    Thanks

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