Error 5.7.705: Access Denied Due to Exceeded Threshold

Microsoft 365 and Office
1

Hello,

Our company provides ticketing system services and uses a mail relay server to send emails on behalf of clients. The clients' domain has both SPF and DKIM set up to allow us to send emails.

Due to an internet issue at our data centre over the weekend, a large number of emails got stuck in the mail relay queue.

After restarting the mail relay this morning, all emails were sent out, but we started receiving NDR messages with the error:

550 5.7.705 Access denied, tenant has exceeded threshold

As a result, many recipients did not receive their emails.

Based on my research, I believe Exchange Online Protection (EOP) filters might have flagged our mail relay server as suspicious due to the high volume of emails sent out and blocked our server.

How can we remove this block?

Thanks in advance.

2

Hey there!

Sorry to hear that your mail relay server got flagged by EOP filters. The error you’re seeing is usually related to sending a high volume of emails within a short period, which can trigger security measures. Here’s what you can do to resolve this issue:

Step 1: Verify Your Mail Relay Server

  1. Revalidate your DKIM and SPF settings: Double-check that your clients’ domain has both SPF and DKIM properly set up and configured correctly. Ensure that these records include your mail relay server IP in the configuration. This step is crucial to ensure that Microsoft doesn’t flag your emails as spam.

Step 2: Check with Microsoft Support

  1. Contact Microsoft Support: Reach out to Microsoft Support to file a ticket regarding the issue. They can help you determine if your mail relay server is indeed flagged and assist in unblocking it. Have your mail relay server IP address ready, as they might need this information to investigate further.

Step 3: Take Proactive Measures

  1. Throttle email sending: Implement a rate limiter on your mail relay server to ensure that emails are sent at a more controlled pace, reducing the likelihood of future blocks.
  2. Regularly monitor your email sending volume: Keep a close eye on the number of emails sent to avoid sudden spikes that might trigger security measures.
  3. Implement stricter email filtering: Tighten your email filtering to reduce the likelihood of sending spam or spam-like emails, which can contribute to getting flagged.

Additional Tips

  • Whitelisting might not work immediately: Even if you get whitelisted by Microsoft, it might take some time for the block to be lifted.
  • Don’t send bulk emails again: Avoid sending a high volume of emails in a short period. Break down the workload or use features like send rate limiting.
  • Monitor your email reputation: Regularly check your email sender reputation to ensure it remains good.

By following these steps, you should be able to lift the block and prevent future occurrences of this issue. Good luck