Unable to send/update mass invite due to 24 hour limit

The 24-hour restriction cannot be bypassed by changing Outlook clients or raising the per-message recipient setting; wait until the rolling quota releases enough capacity, then send the meeting update once.

Which limit applies

Check the account shown in the From field:

• Personal Outlook.com/Hotmail/Live account: Microsoft 365 subscribers are limited to 5,000 recipients per day, 500 per message, and 1,000 daily recipients with whom they have no previous relationship. Limits can be lower based on account history or for non-subscribers.^1^
• Work or school Microsoft 365 account: Exchange Online has a hard 10,000-recipient rolling 24-hour limit. It does not reset at midnight; capacity returns as earlier recipients fall outside the preceding 24 hours. This service-level limit cannot be increased.^2^
• Microsoft 365 calendar meeting: A qualifying outgoing meeting invitation, update, or cancellation supports up to 5,000 recipients.^3^
• Teams meeting created from Outlook: The meeting-recipient limit is 750, not 5,000. A direct 1,800-person update therefore is not supported for this meeting type.^3^

A setting described as “unlimited” does not remove these service limits. For ordinary Exchange Online messages, the default per-message limit is 500 and can only be customized up to 1,000; that setting is separate from the rolling daily quota.^2^

What to do now

1. Do not keep retrying the update.
2. Wait until 24 hours have passed from the sending activity that triggered the restriction. For Exchange Online, access may return gradually because it is a sliding window rather than a fixed reset time.^4^
3. Reopen the calendar event, make all link changes, and send one consolidated update.
4. If sending still fails, record the complete error or non-delivery report:
   • 550 5.7.233 means the organization exceeded its tenant-wide daily external-recipient limit, requiring the Microsoft 365 administrator to review tenant usage.^2^
   • For personal Outlook.com, select Help on the Outlook.com menu bar, enter the error, and use Still need help? → Yes if self-help does not resolve it.^1^

Future large invitations

For a work or school Microsoft 365 environment, have an administrator create an organizational distribution group and use it when designing future invitations. Such a group counts as one recipient for the Exchange Online per-user recipient-rate limit; a personal contact list counts every member separately.^4^

This is not an Outlook.com home-account workaround, and replacing recipients on the existing meeting could affect attendees’ calendar entries. Use the group for a future or safely recreated invitation rather than modifying the current meeting solely to evade its limit.

For future large events where attendance tracking is unnecessary, create the event and choose Response options → turn off Request responses. Outlook then does not record responses in the invitation.^3^

References

1. Sending limits in Outlook.com | Microsoft Support
2. Troubleshoot outbound sending limits and blocked users in Exchange Online
3. Scheduling meetings with hundreds of attendees | Microsoft Support
4. Exchange Online limits