Is there a good server-side webmail solution for people with multiple email accounts, other than logging into each account individually?

What I'm looking for is a way to login once and quickly see the mail that has come in that day, but allow mail to also be separated by account and replies to be sent from the correct account.

Gmail comes close as an external solution in that it allows checking up to 5 pop3 accounts so you can accumulate multiple accounts all in one convenient inbox and then separate both visually using labels on the one screen or click a label to see just mail from that account. The one glitch though is that outgoing mail is actually sent from gmail's server (so though the reply-to is correct for the account, by the headers it's visible that you're using gmail and you have to count on that gmail outgoing mail server being unblocked, etc.)

Is there a server-side solution that could accomplish something as good or better than using gmail to check and reply to mulitple accounts from one convenient interface like this?