- Mailbox Limit: 50GB
- Messages Limit: 1 Million messages per mailbox folder
- Message Size - Outlook for Windows: 150MB
- Message Size - Outlook on the Web: 112MB
- Message Size - Outlook for Mac: 35MB
- Subject length: 255 characters
- File attachments : 250 attachments
- Attachment size limit - Outlook for Windows: 150MB
- Attachment size limit - Outlook for Mac: 35MB
- Attachment size limit - Outlook on the Web: 35MB
*These are the sending limitations set in place on W-Exchange. The recipient's email service may enforce different limitations.
Recipient and sender limits
- Recipient rate limit: 10,000 recipients per day
- Recipient limit per message: 500 recipients
- Message rate limit: 30 messages per minute
For more limits, please see this Microsoft help document.