Outlook blocks certain file types and has a file size limit of 150 Megabytes when sending to another Office 365 mailbox, and 25 Megabytes when sending to non-Office 365 mailboxes.
Blocked file types
View the Blocked attachments in Outlook page for a list of blocked file types and tips for saving files as acceptable file types.
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If you try to send a blocked file type from Outlook, you will receive delivery failure message from the system. If someone tries to send you a blocked file type outside of Office Microsoft 365, their system may not block the message; however, Office Microsoft 365 will block the message and you won't receive their file.
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As a file is attached to a message, its size can inflate beyond the size of the attachment limit due to encoding. It is also possible that the receiving party, if outside of the Office Microsoft 365 system, may have a lower message size limit that will not allow larger attachments to make it through.
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