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

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.

0 comments

43 answers

Sort by: Most helpful
Most helpful Newest Oldest
  1. Anonymous
    2021-07-21T13:38:21+00:00

    Was this answer helpful?

    2 people found this answer helpful.
    0 comments
  2. Anonymous
    2021-07-21T13:52:51+00:00

    That link showed up in our SMTP log and I noticed the article date of 7/19 and figured it was related.

    2021-07-21 08:01:47 52.96.79.130 OutboundConnectionResponse SMTPSVC1 IMISERVER3 - 0 - - 432+4.3.2+Concurrent+connections+limit+exceeded.+Visit+https://aka.ms/concurrent_sending +for+more+information.+[Hostname=CH2PR12MB4310.namprd12.prod.outlook.com] 0 0 161 0 484 SMTP - - - -

    Was this answer helpful?

    1 person found this answer helpful.
    0 comments
  3. Anonymous
    2021-07-20T20:35:08+00:00

    Unfortunately, my issue came back.

    Mailbox unavailable. The server response was: 5.2.252 Sender throttled due to continuous send as denied errors.

    [Hostname=DM6PR12MB4793.namprd12.prod.outlook.com]

    I noticed that for the two mailboxes that have the issue, there are a lot of "SendAs" events, which is baffling because I am using the owner to send out the email, there is no "SendAS" required.

    For the mailbox which doesn't have the issue, I don't find any "SendAs" event.

    I have updated the MS tech, hopefully, they will come out of some permanent fix soon for everyone.

    Was this answer helpful?

    1 person found this answer helpful.
    0 comments
  4. Anonymous
    2021-07-19T07:35:14+00:00

    Hi ahesse47

    I'm following up on this thread, any update?

    Thanks,

    Momo

    Was this answer helpful?

    0 comments
  5. Anonymous
    2021-07-16T08:20:52+00:00

    Hi ahesse47

    Greetings

    Thank you for posting in Microsoft Community.

    To help me better assist you kindly verify how you're accessing your outlook, is it via outlook on the web or outlook desktop client.

    You can try to perform the following steps to help resolve the issue:

    1. Check the Network Settings. Check you internet connection and make sure that the system is connected to a working network.
    2. Check the Account Settings. Check your Outlook account settings to ensure there is no indecent setting causing you to experience this error.
    3. Configure Firewall. It may be possible that your Windows Firewall program is blocking your Outlook application for safety issues. Configure Firewall and allow Outlook to use the internet connection.
    4. lastly try to send mail using a different environment or browser and check to see if the same error appears.

    Please feel free to let me know how it goes

    Regards,

    Momo

    Was this answer helpful?

    0 comments