300: The maximum number of message recipients allowed in the To:, Cc:, and Bcc: fields.
300: The number of recipients that can receive an email in an hour.
1500: The maximum number of recipients that can receive email messages sent from a single cloud-based mailbox in a 24 hour period.
The maximum total size of an email message is 150 megabytes (MB) in Outlook software, 112 MB for webmail software, and 33 MB for mobile devices. The total size includes the message header, the message body, and any file attachments.
150 MB in Outlook software, 112 MB for webmail software and 33 MB for mobile devices.
250: The maximum number of attached files on an email. This includes files embedded in a compressed archive (e.g. ".zip" file).