Whether it's bogus rather depends on the address its sent from and its contents. You could post it here for us to examine, and if you can include the long header that would help, but go through it carefully and remove your own email address before doing this (it may appear in several places in the long header).
However if you are an ex-MobileMe subscriber then it could be related to that. MobileMe subscribers who migrated to iCloud received complimentary extra storage up until September 30 2013. This has now expired. If you have less than 5GB data in iCloud then your storage simply reverts to 5GB.
However if you have more than 5GB data, Backup, Documents and Mail will stop working until you either delete sufficient data to bring you within 5GB or purchase additional storage.
For instructions on purchasing additional storage please see
http://support.apple.com/kb/HT4874
For help in reducing your iCloud data please see
http://support.apple.com/kb/HT4847