I have two email accounts that I use and they receive the same emails. These means they are duplicates of each other. I have back-ups of all-important emails from clients etc. if one server is down I always have a back up even if I accidentally delete an email. I never want to be in a position where I have tell a client that I lost their email.
On my email server I just forward all emails to my
Gmail account so if one server is down I can always use the other one. I can search the archives on either server. If I send an email using Gmail it appears to come from the same account. Periodically I copy my address book to my Gmail account.
If you are one of my hosting clients I can set this up for you. Setting up emails and adding new accounts is free for all of my hosting clients.