gmail's checking of POP3 accounts automatically leaves messages on the server by default (i'm not sure that you can change this). if you have the option to use your non-gmail account as an imap account in outlook, doing so will sync the information between whatever client you use and the server. however, when you make changes to items on the server, gmail's copy is NOT updated (because of POP3).
since going DROID, i have all but forgotten my other non-gmail accounts. gmail handles everything sufficiently enough that if I ever have a need to use one of my old accounts, i can.
even though i've had my hotmail accounts for twice as long as my gmail accounts, i have no problems switching people to the correct account. and if they don't get it (as in make the switch), i can still reply through the old account.
since going DROID, i have all but forgotten my other non-gmail accounts. gmail handles everything sufficiently enough that if I ever have a need to use one of my old accounts, i can.
even though i've had my hotmail accounts for twice as long as my gmail accounts, i have no problems switching people to the correct account. and if they don't get it (as in make the switch), i can still reply through the old account.