Google can and has suspended accounts for the sort of excess activity GmailFS generates. Consequently GmailFS should not be considered reliable for backup purposes. Furthermore, the "Program Policies" prohibit the user to "Reformat or frame any portion of the web pages that are part of the Gmail Service" which is arguably violated by use of GmailFS, which, after all, "reformats" documents transferred via HTTP ("web pages") into data accessible via FUSE.