As well as Gmail does? I really like one particular feature about Gmail that I haven't seen anywhere else. Imagine you're exchanging emails with someone, and you've just replied. However, before receiving a reply from the other person, you realize you have something else to add to your previous message. In Gmail, you can just open up the thread, add a message, and it's perfect. However, in Outlook, it's not so simple. Yes, you can reply to the most recent message from the person, but then they'll have two messages from you. They'll reply to one of those messages, and the other will cease to be part of the thread. Alternatively, you could reply to your latest sent message, but then your own email address shows up in the To: field, and it's rather annoying to have to manually add the desired recipient, especially when there are multiple recipients. Also, if they reply to the first message you sent, the second message you sent will no longer be part of the thread.
Do you understand what I want to be able to do? Is it possible with any local clients, or do I have to use Gmail?