CloudExtend Outlook for NetSuite allows for messages and files to be attached to NetSuite records. If you are attaching a message and files that you received (ie it is already in your inbox) then both will attach with no issues.
If, however, you are composing an Outlook email with attachments you will not be able to attach the files until the email has been sent. The Outlook API requires that the attachments already be on your Exchange Server before they can be accessed via the API.
Therefore we recommend sending the email and opening it in your sent items folder to attach the email and files to NetSuite.