We have not had it happen to us yet, but it has happend before our emails have gone down and we have lost everything and now that emails are more and more to do with our lives we should back them up somewhere away from our computer or away from the cloud.
Using Gmail or google apps:
Check out this program http://www.gmail-backup.com/ or download this software http://home.zcu.cz/~honzas/gmb/gmail-backup-0.107.exe also available into Linux, and it will download your emails form gmail to your local computer so that if gmail ever deleted anything on your or you lost everything on day you would still have local copy of emails.
Go to https://cp.blacknight.com/ login using your username and password,
Click on backup on left panel
Add new backup
Name the backup and click all the boxes on the left of hosting packages
Locate your pst file, this is where all your emails are stored,
* By default on XP it is located in;
C:\Documents and Settings\%username%\Local Settings\Application Data\Microsoft\Outlook\
For Windows Vista the default is;
* You can also locate the file by using;
Right click the root folder (probably Outlook Today)-> Properties-> button Advanced-> field Filename
Copy all those files and folders over to an external hard disk or another computer as regular as possible.
Using Outlook Express:
Bit more complicated but follow outlook KB and should explain it, http://support.microsoft.com/kb/270670
Using Blacknight/Digiweb/any other hosting compay and Outlook
It would be good to do both the Using Outlook and the Using Blacknight steps.
Visit, http://mozbackup.jasnapaka.com/ or download from following link http://downloads.sourceforge.net/mozbackup/MozBackup-1.4.9_EN.exe?download and run backups,
n.b: ALL THESE BACKUPS SHOULD BE BACKED UP OFF SITE OR ONTO ANOTHER DEVICE, please do not use the same computer to back these files up to, and if your using external hard disk get two hard disk do not rely on one, and if your using tapes do not.
Any questions please do contact me