What are the size limits for my emails?

Message Size Limits

The message size limit for Exchange Online is 25MB, including attachments. This size limit applies to all messages (inbound, outbound, and internal) and can’t be amended.

The default attachment size limit for a single attachment is 10MB.

Messages larger than 25MB will not be delivered, and the sender will receive a Non- Delivery Report (NDR).

Message size limits are necessary to prevent large messages from negatively affecting system performance and to ensure fast message delivery for all users.

 

Recipient size limits

These limits apply to emails sent within an organisation as well as to messages delivered to external organisations.

Business Email Lite (powered by Microsoft Office 365)

  • Each Exchange Online mailbox can send messages to a maximum of 1,500 recipients per day.
  • An email message can be addressed to a maximum of 500 recipients.

Microsoft Office 365

  • Each Exchange Online mailbox can send messages to a maximum of 10,000 recipients in any rolling 24 hour timeframe.
  • An email message can be addressed to a maximum of 500 recipients.

To stop users from sending unsolicited bulk messages, Exchange Online has restrictions that prevent users and applications from sending large volumes of email.

To send legitimate bulk commercial email (for example, customer newsletters) you should use third-party providers that specialise in these services.


Message Rate Limits

To maintain service and help guard against inappropriate use, users can send only 30 messages per minute.

If you submit messages at a faster rate, Exchange Online will deliver the messages but will queue them at the server and will manage the rate of delivery.

 

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