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unable to send an email

Glenn Maxwell 13,841 Reputation points
2026-06-26T06:24:50.5566667+00:00

Hi All,

I am using Microsoft 365 E5 licenses. One of our users is attempting to send an email or calendar invitation to approximately 5,000 recipients, but the message is not being sent and appears to be hitting an Exchange Online recipient limit.

My understanding is that Exchange Online has a recipient limit that applies to the total number of recipients in the To, CC, and BCC fields.

Could someone please clarify the following:

  1. What is the maximum number of recipients allowed per email message in Exchange Online (combined To, CC, and BCC recipients)?
  2. Does the same recipient limit apply to Outlook calendar invitations?
  3. Is the default recipient limit 500 or 1,000 recipients per message for Microsoft 365 E5 users?
  4. If a user sends an email to a Distribution List containing more than 5,000 members, Do restriction needs to be imposed on the DL, i.e specific senders can only send email to the DL.
Exchange Online
Exchange Online

A cloud-based service included in Microsoft 365, delivering scalable messaging and collaboration features with simplified management and automatic updates.

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Answer accepted by question author

Hani-Ng 12,335 Reputation points Microsoft External Staff Moderator
2026-06-26T07:04:24.4066667+00:00

Hi Glenn Maxwell

Based on the current Exchange Online service limits:

  • Email recipient limit (To + CC + BCC): The default limit for a mailbox is 500 recipients per message, but administrators can customize this up to 1,000 recipients per mailbox. This limit applies regardless of the Microsoft 365 license plan, including Microsoft 365 E5. To customize recipient limit, you can see: Customizable Recipient Limits in Office 365 | Microsoft Community Hub

User's image

  • Meeting invitations and updates: Exchange Online uses a separate limit for meeting messages. The maximum number of recipients for a meeting invitation, update, or cancellation is 5,000 recipients.

User's image

  • Recipient rate limit: Exchange Online also enforces a 10,000-recipient per 24-hour sending limit per mailbox. This is different from the per-message recipient limit.

Regarding Distribution Lists (DLs):

  • For recipient limit calculations, a Distribution Group stored in the organization's address book (GAL) is counted as one recipient when it is added to a message.
  • Exchange Online supports Distribution Groups with up to 100,000 members
  • For Distribution Groups containing 5,000 or more members, Microsoft requires either Delivery Management (restricting who can send to the group) or Message Approval/Moderation to be configured.

User's image

If the user is attempting to send directly to approximately 5,000 individual recipients, they will likely exceed the mailbox recipient limit. If the intent is to reach a large audience, using a properly configured Distribution Group or another bulk-mailing solution may be more appropriate.

For reference:

To better understand the scenario, is the user sending the message directly to about 5,000 recipients, or sending it to a Distribution List that contains more than 5,000 members?

I hope this information helps and look forward to your response!

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