Ever since switching to Gmail in 2009 I have been trying to find a reliable long term backup solution. First I used GMail Backup (but it had problems with large folders, and setting messages as read), then switched to Gmail Keeper (but it started crashing / using up large amounts of CPU time).
I have now switched to Spanning Backup. It is a subscription service ($35 per year) but does also backup contacts, calendars, documents as well which is handy. I also like that it actually shows an inbox type view allowing you to see all backup messages, filter by label, and tick a box to restore them.
Seems to work very well for a single account however, I have had some issues trying to use it on domain accounts. As best I have been able to determine if you want to restore messages on a domain account you need to login to the Spanning control panel as that user with their password, i.e. logging in with a Google Apps “Super Admin” account does not work. Possibly this might be due to not activating the backup service on the “Super Admin” account itself, but this is not something I want to do because the Admin account does not need backing up (and it is an extra cost to do so).
Spanning Backup also have an affiliate program where they give you a code which allows others to get the $35 per year discount rate (normal cost $40), and also saves you $5 as well.
Discount Code: 7K8HAN