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
    2021-07-21T16:10:22+00:00

    Having the same issue; account is already business standard; problem started at 9:15 CDT this morning. Emails aren't being sent even if the from / reply to is the actual account, not a "send-as", although the bounce message remains the same.

    Ticket opened with MSFT as well.

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  2. Anonymous
    2021-07-21T15:08:23+00:00

    Investigating potential workarounds led me to delete our SMTP service account and recreate it with the same name and password as our original configuration and it seems to be working now.

    Obviously this isn't an ideal fix and I'm not sure how long it will last but maybe it can help some of you guys hobble along until Microsoft fixes their issue!

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  3. Anonymous
    2021-07-21T14:36:49+00:00

    Thanks Frank Wulfers, at least in our case it is actually related to the new limitations, we had to create a new email account for each application.

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  4. Anonymous
    2021-07-21T13:49:58+00:00

    We are having the same issue now. Started this morning around 9am EST. Unable to send emails through our internal SMTP server...Microsoft must've changed something...gah.

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  5. Anonymous
    2021-07-21T13:47:25+00:00

    Thank you Frank.

    I think this is somewhat related to our issues. However, from the article the error message should be "432 4.3.2 STOREDRV.ClientSubmit; sender thread limit exceeded", not "550 5.2.252 Sender throttled due to continuous send as denied errors.". And the behavior should be delay in email sending, not rejecting connection completely.

    It could be when MS deploy this new throttle, they mess up something else, now we have an unexpected throttle.

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