Lost email and email accounts

One day out of the blue, my email and email accounts were gone when I opened my Outlook for Mac 2011.  After a period of stress, I reinstall the missing email accounts.  My Exchange account came back fully populated with sub folders and email but my Comcast account only partially re-stored.  In fact all previous email in my "inbox" was gone with the exception of the current messages that day....all previous emil from days past was gone.