Send & Receive Issues

How Exchange Online Recipient Limits Work with Send As Permissions

Natalie Taylor Sep 28, 2026 869 views

Question details

An organization wants to know whether Exchange Online's recipient rate limit applies to the delegate or the represented mailbox when a user sends thousands of messages using Send As permission.

How Exchange Online Recipient Limits Work with Send As Permissions

Product: Exchange Online
Device & OS: not provided
Scenario: A delegate uses Send As permissions to send a large volume of messages representing another mailbox.
Observed behavior: The recipient rate limit is applied to the mailbox shown as the sender (the represented mailbox), rather than the delegate's personal mailbox.

Before you start

Before planning large email campaigns, verify the exact recipient rate limits configured for your Microsoft 365 tenant, as the default limit is typically 10,000 recipients per 24 hours per mailbox.

Solution 1Recommended

Understand and Manage 'Send As' Recipient Limits

This outlines how Exchange Online calculates recipient rate limits for delegated sending and how to avoid hitting these thresholds.

When a delegate uses 'Send As' permissions to send an email, Exchange Online associates the recipient rate limit with the mailbox that appears as the sender.

Consequently, if a delegate sends 10,000 messages on behalf of a shared or represented mailbox, the represented mailbox itself will reach its recipient limit, while the delegate's personal account limits remain unaffected.

Identify the sending mailbox

Determine the exact email address being used in the 'From' field. This is the account that will accrue the recipient count for rate-limiting purposes.

Monitor recipient counts

Track the total number of recipients addressed by the represented mailbox within a rolling 24-hour period. Ensure this number does not exceed the 10,000-recipient threshold.

Use bulk email services for large campaigns

If you need to send messages to more than 10,000 recipients, utilize a dedicated third-party bulk email provider instead of standard Exchange Online mailboxes to prevent the sender address from being blocked.

Understand and Manage 'Send As' Recipient Limits

Shared Mailbox Limitations: Shared mailboxes are subject to the exact same recipient limits as regular user mailboxes. Reaching the limit will restrict the shared mailbox from sending further emails for up to 24 hours.

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Frequently Asked Questions

What is the standard Exchange Online recipient rate limit?

Exchange Online typically limits users to sending emails to a maximum of 10,000 recipients per day. This limit is in place to prevent spam and ensure system health.

Does 'Send on Behalf' work the same way as 'Send As' for rate limits?

Yes, whether you use 'Send As' or 'Send on Behalf' permissions, the recipient limits are generally charged against the mailbox that is represented in the sender field, not the delegate.

What happens when a mailbox reaches its recipient limit?

When the recipient limit is reached, the mailbox is temporarily blocked from sending new emails. Users will receive a non-delivery report (NDR) for any new messages attempted during this 24-hour block period.

How can I send bulk emails without hitting the Exchange limit?

For legitimate bulk email scenarios, such as marketing newsletters or company-wide announcements exceeding 10,000 recipients, it is recommended to use specialized bulk mailing services (e.g., Mailchimp, SendGrid) rather than relying on standard Exchange Online mailboxes.

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