NDR 550 5.1.90 – Daily Recipient Limit Exceeded for Service Account | Urgent Assistance Required

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As a forum moderator, I’m here to help guide discussions and share insights based on Microsoft documentation and community knowledge. Although I don’t have direct access tothe back-end system, I’ll do my best to support you with practical steps and point you to the appropriate resources.

Hi @Priyadharshini K

The 550 5.1.90 NDR indicates that the sender has exceeded the daily limit for the number of recipients allowed in Exchange Online. To see the limit, view here.

This typically occurs when sending a high volume of emails or using large distribution lists (including BCC). As a result, further outbound messages are temporarily blocked, and the sender must wait until the limit resets or reduce the volume of recipients before sending again.

What you can do now is stop sending emails temporarily, you’ve hit the daily limit, so further sends will continue to fail.

Wait ~24 hours for the recipient limit to reset, retry with smaller batches and avoid large BCC lists.

If you do not send bulk email, there's a chance your account has been compromised and is being used to send spam.

If that's the case, immediately contact your admin and inform them about your situation. You can give them this article or further steps: Responding to a Compromised Email Account - Microsoft Defender for Office 365 | Microsoft Learn

I hope this information helps.

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Here's a polished LinkedIn post:

🚨 Received "550 5.1.90" when sending internal emails in Exchange Online?

Error:

Remote Server returned '550 5.1.90' Your message can't be sent because you've reached your daily limit for message recipients.

💡 Important Tip

If you're sending emails to a large number of internal recipients, consider using a Distribution List (DL) instead of individual email addresses.

Why?

✅ For the recipient rate limit, a Distribution Group stored in the organization's address book counts as a single recipient. ✅ This helps reduce the recipient count against the sender's daily limit. ✅ Personal distribution lists stored in a user's Contacts folder do not provide this benefit, as each member is counted individually. [techcommun...rosoft.com]

Best Practice

• Use organization-managed Distribution Lists for internal communications.
• Avoid sending large emails to hundreds of individual recipients.
• Review automated workflows and service accounts that send high-volume emails.

A small change in how recipients are addressed can help prevent unnecessary NDRs and improve mail flow efficiency.

#Microsoft365 #ExchangeOnline #M365 #ExchangeAdmin #ITPro #EmailAdministration #DistributionLists #TechTips #MicrosoftExchange [techcommun...rosoft.com], [learn.microsoft.com]