Sudden failure to send emails through specified SMTP server with python script

Anonymous

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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43 answers

Anonymous

2021-07-20T15:00:58+00:00

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
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Anonymous

2021-07-20T15:17:27+00:00

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.
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Anonymous

2021-07-20T16:13:47+00:00

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..
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Anonymous

2021-07-20T16:29:21+00:00

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.
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Anonymous

2021-07-20T16:43:26+00:00

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.
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