If the attachment is not in the correct format, the download and.or upload could fail. This is all part of a security system which may emails services are using to reduce or eliminate spammers from sending files of folders to unsuspecting contacts. Also if the file is too large, you may not even see a message stating that the file is too large and cant be downloaded or uploaded. Again all in an effort to secure email services. The typical file size lime can range from 2MB to 6MB anything larger may not be supported so check with your email service for what types of files can be sent and the max size of the file.
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