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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.
I just did a few more tests and still getting the same errors and rejected emails... I can't image this is tenant specific and they have to run these commands for any accounts that have problems.
The account we are using for these emails already is a Business Standard account and mailbox looks ok.
MS support just called, they said they ran some command on the backend. looks like it fixed the issue, I don't have the error message anymore and I can send out emails using SMTP relay.
However, they did run the same command a couple of times in the last couple of days, but that didn't fix the issue. Not sure if they did something new this time, or it's just the throttle expired.
I will monitor this and update back.
We ended up going into Exchange Online and changing the email account type from Business Basic to Business Standard. I don't know if this was truly the solution or if it was timing or what, but we noticed that it said a mailbox was not setup for the account (even though I could view the mailbox for the account). We can now send email again, but this doesn't feel like a permanent (or necessary) solution.
This started happening for us July 15th. We use an IIS SMTP server for sending out automated invoices, purchase orders and other emails that IIS relays to Microsoft 365. Has been working great until last week. Sometimes emails get sent out but other times emails get dumped in the badmail queue on the SMTP server. And they won't resend.
Action: failed
Status: 5.2.252
Diagnostic-Code: smtp;550 5.2.252 Sender throttled due to continuous send as denied errors. [Hostname=CH2PR12MB4310.namprd12.prod.outlook.com
Need to find a fix for this asap..