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
    2021-07-22T14:32:27+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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  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
    2021-07-22T14:36:39+00:00

    Yea, I do about 100 emails a day max.

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  4. Anonymous
    2021-07-22T14:55:45+00:00

    but if they all leave at the same time 100 within a minute that will cause your account to throttle.

    either send to a distribution list (or) set delays on how often they leave (If they all leave at the same time)

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  5. Anonymous
    2021-07-22T15:01:40+00:00

    I am not sure if the 30-emails-per-minute is the cause for our issue.

    From the article, "Exceeding the per minute limit causes email delivery delays, any excess in message submission will be throttled and successively carried over to the following minutes.", it looks like it should just delay the sending, not to reject it completely.

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