Some emails being delayed

Question

I keep getting the following message for a number of emails being sent (not all) :

Delay reason: SMTP error from remote mail server after pipelined end of data

  The mail server [....] has been temporarily rate limited due to IP reputation.

What does this mean and how do I fix it

Answer 1

Hi Lonnae Harris

Thank you for reaching out to Microsoft Q&A

As far as I know, this is a recipient-side temporary deferral: the remote mail server is rate limiting your sending public IP because its IP reputation is currently considered risky. It’s not an Outlook client problem so the delivery should resume once the recipient server lifts the throttle and your server retries.

Given this, you can try the below approach to see if it can help you:

1. Confirm the sending public IP shown in the delay/bounce and whether it happens mainly to Outlook/Hotmail/Live recipients.
2. If it’s Microsoft-hosted recipients, submit the IP to Microsoft’s delist portal: Delist IP
3. Reduce burst sending volume (spread sends over time) and allow normal SMTP retries
4. If you send via Exchange Online, verify you’re not hitting service sending limits that can contribute to throttling behavior.

Hope my answer will help you.

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Answer 2

The message you are encountering indicates that your emails are being delayed because the mail server has temporarily rate-limited your IP address due to its reputation. This situation arises when there is suspicious activity detected from your IP, often linked to sending a high volume of emails or having a poor sender reputation.

To resolve this issue, consider the following actions:

1. Check IP Reputation: Use online tools to assess the reputation of your sending IP address. If it appears on any blocklists, you may need to request its removal.
2. Limit Email Sending Volume: If you are sending a large number of emails, try to distribute them over a longer timeframe to avoid triggering rate limits.
3. Maintain a Clean Email List: Regularly update your contact list to remove invalid or inactive email addresses, which can enhance your sender reputation.
4. Monitor Bounce Rates: Keep track of your email bounce rates, as a high bounce rate can adversely affect your reputation.
5. Contact Your Email Service Provider: If the problem continues, reach out to your email service provider for assistance and further insights regarding your sending practices.

By following these steps, you can improve your IP reputation and reduce the chances of experiencing email delays in the future.