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
    2021-07-21T14:36:49+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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  2. Anonymous
    2021-07-21T13:52:51+00:00

    That link showed up in our SMTP log and I noticed the article date of 7/19 and figured it was related.

    2021-07-21 08:01:47 52.96.79.130 OutboundConnectionResponse SMTPSVC1 IMISERVER3 - 0 - - 432+4.3.2+Concurrent+connections+limit+exceeded.+Visit+https://aka.ms/concurrent_sending +for+more+information.+[Hostname=CH2PR12MB4310.namprd12.prod.outlook.com] 0 0 161 0 484 SMTP - - - -

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  3. 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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  4. 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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  5. Anonymous
    2021-07-21T13:38:21+00:00

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    2 people found this answer helpful.
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