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

I have this issue also, I use a scripted email to reply to tickets...

my error is

SMTP Error: data not accepted.SMTP server error: DATA END command failed Detail: 5.2.252 Sender throttled due to continuous send as denied errors. [Hostname=BYAPR15MB2199.namprd15.prod.outlook.com]

I use tls, SMTP, smtp.office365.com, port 587, authorize and send-as / from using the username and password on the account.

Everything was working flawlessly until recently it became unreliable. This account did send out my inventory feeds this morning

but I'm worried because at the moment its having the issue above.

Does the From name need to be blank? it sporadically works both ways by setting the From the accounts email. and either

setting the From Name to be blank or to the actual account display name.

just trying to resolve the 'continuous send as denied errors' !

Thank you.

I went through all my scripts and set the FromName to specifically match the accounts display name.

There were a few legacy (descriptive) FromName(s) on some. Not sure if this is the answer but my apps have sent a few responses out as needed. We will see if it continues to do so.... Maybe Microsoft no longer ignores the FromName?

Mine seems to have started working around the same time as Franks... coincidence?

Just glad to have it all working.

OK not working, still sporadic, I'm beginning to believe this is a volume on account issue. looks like the

'data not accepted.' lasts for ~6hrs

looking into other options.

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.