Earlier this year, we detailed how to automatically forward your email to Gmail as a backup solution. Doing that proved to be very useful to me when my main mail server had a temporary freak-out this morning.
Long story short: a misconfigured spam email started endlessly forwarding itself from my Lifehacker work account to my main account and filled my inbox beyond its capacity, generating bounce messages to everyone who contacted me and rendering my email address inaccessible to Outlook or web mail access. I was away from my machine when the overfilling started, so didn't realise until the damage was well and truly done.
Despite those problems, however, the auto-forwarding rule I had set up to copy mail to Gmail continued to work, which meant I still had accessible copies of everything that had been sent to me during that time, and an opportunity to figure out what went wrong. The experience didn't convince me to switch to Gmail entirely -- I still prefer a desktop client and control of my mail domain -- but as a backup, it worked pretty much flawlessly. Hit the original Lifehacker 101 post for details on how you can do the same.