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
    2021-07-22T14:36:39+00:00

    Yea, I do about 100 emails a day max.

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  2. Anonymous
    2021-07-22T14:34:40+00:00

    the answer is here in the article posted previously:

    https://docs.microsoft.com/en-us/exchange/troubleshoot/send-emails/smtp-submission-improvements#new-throttling-limit-for-concurrent-connections-that-submitmessages

    We had to have our developers create distribution lists they had reporting subscriptions active which were maxing out the 30 emails per minute limit which is causing the never ending throttle and having to open a ticket to have O365 support run RBAC to Unthrottle the account. find out how many emails your program is sending per minute most likely you'll have a bottle neck there too.

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  3. Anonymous
    2021-07-22T14:32:27+00:00

    I've had a ticket in with Microsoft for the past couple of days, haven't heard anything back since trying to get my ticket escalated. But the account having the same issue's as everyone else, just started working last night. I did find a work around, I added another account to send as that account and was able to use different credentials and send out as the needed account.

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  4. 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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  5. 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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