I'm not on gmail, so I don't know if this is the same as conversation-style, but Thunderbird has provided the ability to view emails in a threaded view for years. Apparently you can also configure Tbird to maintain this threaded view when sorting by date, subject, from, to, etc.:
Tbird's threaded view is nowhere near as intelligent as Google's threaded view. When an email client arbitrarily adds a "Re:" is messes it up. Conversation-style view is more or less useless when split up among multiple conversations.
When an email client arbitrarily adds a "Re:" it messes it up.
I'm pretty sure Thunderbird uses the Message-ID and In-Reply-To headers to create the threads, not the subjects. But some people don't always use the Reply function, or Reply to an old email when they want to start a new conversation. Maybe Gmail has some logic to get around these limitations.
In Thunderbird 3, we use a combination of the two models, as some mail providers (Yahoo! for example, IIRC) strip away the right headers. Thunderbird 3's threading is way better than Thunderbird 2's.
TB3 doesn't support conversations out of the box, but I'm thinking about doing an add-on to experiment with that. With our new global database, it should be possible to do something interesting.
If you don't mind paying for it, Postbox (http://www.postbox-inc.com/) does support this feature. That said, I find it quite annoying.
I know this sounds crazy, but the only non-Gmail chat client I like is the one that comes with Opera. It's every feature of Gmail except conversations--which, annoying, is the one that I also badly wish I had.
I think TB3 has a way to do this. However, its still pretty rudimentary. For example, if Im in threaded view and the thread is closed, I can click on the first email of the thread and it shows me the conversation-style message. However, it seems like each conversation has a limit and so after a certain legth of the message, it shows ...
if you have too many messages in the thread then you just end up with
PersonA
...
PersonB
...
Useless.. but hopefully something that will be customizable before 3.0 is released.
Does anyone know if TB3 supports this? If not, does any other email client?