Email limits and message limitations in Office 365

By: Kareem Printer Friendly Format    


Recently a customer saw this error message "This message can't be sent. You've reached the limit on the number of messages that can be sent in a 24-hour period." in her OWA while trying to send an email. She had no clue on what is happening. After some research this is what we found out.

She was using her email account as SMTP Relay server login, to send out emails from her webserver. At the same time, she is using the same email account as her personal email. This is why she reached the daily number of email messages limit in a day.

Here is a summary of message limits and recipient limits in Office 365

  • The maximum total size of an e-mail message. The total size includes the message header, the message body, and any file attachments is 25MB
  • The maximum number of file attachments allowed in an e-mail message is 125 attachments
  • The maximum number of text characters allowed in the subject line of an e-mail message is 255 characters
  • The maximum number of message body parts that are allowed in a MIME multipart message is 250 parts
  • The maximum number of forwarded e-mail messages that are allowed in an e-mail message is 30 messages
  • The maximum number of message recipients allowed in the To:, Cc:, and Bcc: fields is 500 recipients
  • The maximum number of e-mail messages that can be sent from a single e-mail client per minute. The client is identified by the user account is 30 messages per minute
  • The maximum number of recipients that can receive e-mail messages sent from a single cloud-based mailbox in a 24 hour period is 1500 recipients in a day.


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