Send & Receive Issues

How to Fix Microsoft 365 Email Sending Limits and Pending Delays

Kushani Nimanthika Oct 13, 2026 869 views

Question details

The user wants to understand and resolve the issue where Microsoft 365 external emails remain pending for 12 to 24 hours due to exceeded outbound sending limits.

How to Fix Microsoft 365 Email Sending Limits and Pending Delays

Product: Microsoft 365 Exchange Online
Device & OS: not provided
Scenario: Sending emails to external recipients or large recurring recipient lists.
Observed behavior: External emails remain in a pending state for 12 to 24 hours because the Microsoft 365 outbound sending rate limits have been exceeded.

Before you start

Ensure you have administrator access to your Microsoft 365 tenant to check outbound spam policies and review recent sending activity reports in the Exchange Admin Center.

Solution 1Recommended

Use Distribution Groups for Recurring Recipient Lists

Using distribution groups stored in the shared address book can help bypass individual recipient limits, as a group counts as a single recipient.

Microsoft 365 imposes strict outbound sending limits to combat spam. If you frequently email the same large group of people, adding them individually can quickly exhaust your daily recipient limit, causing outgoing emails to stall for up to 24 hours.

Open Exchange Admin Center

Create a Distribution Group

Go to the 'Recipients' section and select 'Groups'. Choose to add a new distribution group and add your recurring recipients to this new group.

Send via Group Email

Compose your email and put the distribution group's email address in the recipient field instead of adding each recipient individually.

Use Distribution Groups for Recurring Recipient Lists

Limit Reduction: A distribution group stored in the organization's shared address book counts as just one recipient toward your Microsoft 365 sending limits.

Solution 2

Contact Microsoft Support for Throttling Review

If emails are still delayed and your recipient lists vary, Microsoft must verify if the throttling is tenant-wide, user-specific, or triggered by spam controls.

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Frequently Asked Questions

Why are my Microsoft 365 external emails pending for up to 24 hours?

This typically occurs when your account exceeds the Microsoft 365 outbound sending rate limits (such as sending too many emails per minute or day). The system temporarily throttles the account to prevent spam, causing new outgoing emails to remain pending until the limit window resets.

What is the recipient rate limit in Exchange Online?

By default, Exchange Online limits a user to sending messages to a maximum of 10,000 recipients per day. Additionally, there is a limit on the number of messages you can send per minute. Exceeding these triggers automatic throttling.

How can a distribution group help with email sending limits?

If you frequently send emails to the same large group of people, placing them in a distribution group within your organization's shared address book counts as only one recipient toward your limits, significantly reducing the risk of being throttled.

Can I use a distribution group for all my bulk emails?

No. Distribution groups are only practical for recurring, static recipient lists. If your recipient lists vary greatly from message to message, using a distribution group is not viable, and you may need a dedicated third-party bulk email marketing service.

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