I've worked around the duplicate email issue. I didn't see this suggested anywhere else, but so far I think it's the best solution that's ever been proposed.
TWO EMAIL ACCOUNTS.
One for outgoing and one for incoming when using POP clients. For the webmail client you can obviously log into the incoming account and use that for sending as well. Then you'll get those sent messages back on your client later which can actually be a god thing (as long as you filter them into the sent mail folder client-side).
So what I've done was to create a new account, called for example "
[email protected]" and set the original account to forward all mail to that account. Then I simply changed the POP account on my client to [ppicl up mail there while still sending using the previous address.
To wrap it all up (optionally), on that original (sending) account I'm also including filters to delete any mail FROM my domains. That way nothing I send gets duplicated on that gmail account either. You can implement just this filtering suggestion, but then you get an error every time you send mail using the web UI.