I'm not really a fan of MS Outlook, but I am forced to use it at work. It does have support for conversation grouping though. Just do "arrange by" -> "show as conversations" from the context menu.

Apple Mail has it. I think you can tell it whether you want to see newest-first or the reverse, as well.

Actually, Mail.app's lack of conversation view was one of its definitive dealbreakers for me.

In particular, it doesn't include you or your sent mail in the conversation (http://i.imgur.com/Atkcu.png). It only lets you expand the email quotation to let you dig through nested context (http://i.imgur.com/1Zj2e.png).

Compare this to gmail (http://i.imgur.com/mLel3.png) that actually handles it as a conversation. It's one of the reasons I use Mailplane (thin wrapper around gmail) instead of Mail.app.

I too was frustrated by Mail.app's lack of a proper conversation view. Turns out, there's a setting to show messages you sent. In the "Viewing" section of Mail.app's preferences, enable "Include related messages". http://imgur.com/i5Eaq

This seemingly minor preference is what makes Mail.app useable.

Actually, Mail.app can include your own mail in a conversation, but only if you ask it to: select View->Show Related Messages.

Opera seems to have it too, but I don't use it much. It also has had "labels" (as opposed to folders) and message indexing for quite some time, I believe this was one of its main selling points.

What's the difference between conversations and threads?

I use gmail, and I use Outlook and PINE and Netscape Mail and Eudora etc and I can't work out what was improved.

Conversations typically trim portions of messages to make it look you only see what people actually type out. It strips things like headers, signatures, replies, etc.

Threads are a sort of pre-Web 2.0 way of doing things. The messages are linked together in the tree portion of the UI but are still viewed individually in the viewing pane. They aren't stacked together like they are in a typical conversation view.

Conversations are a more modern, succinct take on what threads were trying to be.

mutt's index view, ordered by thread.

Does mutt include your sent mail in that view? This is one of the gmail features I love. I don't have to dig around to see the flow of a conversation with gmail.

Also, if I receive a message, reply to it and archive that thread it goes away. But if that person reply's again it brings the whole conversation back to the inbox so I can see the previous messages as well.

As someone who uses the inbox as a partial todo list that is amazing. It makes it difficult to switch from gmail, although I've been using mu4e[1] inside emacs.

[1] http://www.djcbsoftware.nl/code/mu/mu4e.html

To include your outgoing messages in threads, just set up a hook that adds an Fcc: +inbox header. I used to copy all outgoing messages to a separate +sent folder, but that didn't turn out to be very useful.

Thunderbird has a conversation view (needs to be turned on in the settings)

Outlook has had that since 2003, though it was not very functional until 2010. It is not enabled by default.