Configuring a job to 'run as an alternate user' will cause the respective job to process and export as the alternate user with a process of impersonation. We recommend against this in most instances as there are many potential permission issues that can arise.
If you wish to run all jobs using a given network account, then we highly recommend changing the Windows Service properties to 'run as...' the desired account.
Be aware that if the provided user does not have permissions to access the current server/machine and/or have permissions to write to the destination then jobs will fail to run.
Link to this article http://umango.com/KB?article=60