This limit applies whether you are adding one large attachment that is greater than 20 megabytes (MB) or several attachments whose sum total size is greater than 20 MB. This limit prevents your computer from continually trying to upload very large attachments that exceed the limits of most Internet service providers. You receive this error message because Outlook 2013 and later versions have a default attachment size limit of 20 megabytes (20480 KB) for Internet email accounts. Internet email account (POP3, IMAP, HTTP) This problem occurs for one of the following reasons, depending on the kind of email account that you are using. Try putting the file in a shared location and sending a link instead. The file you're attaching is bigger than the server allows. When you add an attachment to an email message in Microsoft Outlook 2013 or later versions, you receive the following error message:
Attachment size exceeds the allowable limit error when you add a large attachment to an email message in Outlook
