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Need help resolving "Remote server returned '550 5.7.705 Service unavailable. Access denied, tenant has exceeded threshold."

Anonymous
2025-03-15T16:00:22+00:00

Hello,

We are running in a hybrid Exchange 365 and on-prem Exchange model. We had an issue in which our on-prem server was mistakenly opened to allow inbound as a relay. We had an actor send about 2600 emails out which were then redirected to our Exchange 365 to go out from there which created an alert and caused Microsoft to block all outbound email from our tenant. We have since mitigated the issue with our on-prem server to prevent external connections except from Microsoft 365 servers. Per the Microsoft support site (https://support.microsoft.com/en-us/topic/ndr-error-codes-550-5-7-703-550-5-7-705-550-5-7-708-and-550-5-7-750-f5675801-1846-4d1c-9599-5b4e26a9175d ) we need to have Microsoft remove the block but we cannot figure out how to request that unblock.

Can someone please assist and provide guidance?

Below is the NDR we are getting back from Microsoft when we try to send emails.

Thank you in advance!

Delivery has failed to these recipients or groups:

******@xyz.com
Your message wasn't delivered because the recipient's email provider rejected it.

Diagnostic information for administrators:

Generating server: MW4PR06MB8249.namprd06.prod.outlook.com

******@xyz.com
Remote server returned '550 5.7.705 Service unavailable. Access denied, tenant has exceeded threshold. For more information please go to http://go.microsoft.com/fwlink/?LinkId=526653 S(7136) [CH2PPF0ED1609B6.namprd06.prod.outlook.com 2025-03-15T15:30:43.637Z 08DD6211C51D1720]'

Original message headers:

Received: from MW4PR06MB8249.namprd06.prod.outlook.com

 ([fe80::3ce5:ef13:e7ac:ee1]) by MW4PR06MB8249.namprd06.prod.outlook.com

 ([fe80::3ce5:ef13:e7ac:ee1%4]) with mapi id 15.20.8511.026; Sat, 15 Mar 2025

 15:30:43 +0000

MIME-Version: 1.0

Content-Type: text/plain

Date: Sat, 15 Mar 2025 15:30:43 +0000

Message-ID:

Subject: Test out
Microsoft 365 and Office | Subscription, account, billing | For business | Other

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  1. Anonymous
    2025-03-15T20:43:59+00:00

    Dear Lee Anderson II,

    Good day! Thank you for posting to Microsoft Community.

    Your tenant has exceeded the amount of emails that can be send due to antispam system blocking outgoing mails. This happens generally when any email address is used to send a huge number of emails from a particular tenant. I understand your query here and to request the unblocking of your outbound email from your tenant due to the "Remote server returned '550 5.7.705 Service unavailable. Access denied, tenant has exceeded threshold error, I sincerely recommended to contact Microsoft Support directly. If you are an admin or have admin access to your organization Tenant's Microsoft 365 admin center page, see Get support - Microsoft 365 admin | Microsoft Learn. So that, our dedicated online support team will help you unblocking

    Image

    Note: if you are an end user, I sincerely recommend contacting your organization admin to raise a support ticket through Microsoft 365 admin center.

    Thank you for your precious time and kind understanding. Have a nice day.

    Sincerely,

    Libeamlak | Microsoft Community Moderator

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