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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 features that help users manage their subscriptions, account settings, and billing information.
Locked Question. This question was migrated from the Microsoft Support Community. You can vote on whether it's helpful, but you can't add comments or replies or follow the question.
This seems to be the only thread related to this particular error that I can find online. I am assuming there is some new throttling feature in Exchange Online that blocks an account? I'd love to figure out how to disable this for one account that we use to send a high volume of emails.
I also noticed from the audit log that the emails sent by those accounts are "SendAs". But the user and SendAs user are the same email address, why those emails are treated as "SendAs" emails?
TimeStamp : 2021-07-20T10:48:46
Action : SendAs
User : ******@domain.com
SendAs : ******@domain.com
Status : Succeeded
SentBy : ******@domain.com
TimeStamp : 2021-07-20T10:48:46
Action : SendAs
User : ******@domain.com
SendAs : ******@domain.com
Status : Succeeded
SentBy : ******@domain.com
TimeStamp : 2021-07-20T13:44:30
Action : SendAs
User : ******@domain.com
SendAs : ******@domain.com
Status : Succeeded
SentBy : ******@domain.com
TimeStamp : 2021-07-20T13:44:30
Action : SendAs
User : ******@domain.com
SendAs : ******@domain.com
Status : Succeeded
SentBy : ******@domain.com
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
Am Seeing the same issue. By any chance are you using IIS SMTP server to replay messages?
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]