The appliance will try once to upload the file; if upload is not successful, for example because of connectivity problems, the file may not be uploaded. If the failure was because the file analysis server was overloaded, the upload will be attempted once more. Reference: https://www.cisco.com/c/en/us/support/docs/security/email-security-appliance/118796- technoteesa-00.htmlIn this question, it stated "the network is congested" (not the file analysis server was overloaded) so theappliance will not try to upload the file again.