I tried using Evolution a few years ago, but repeatedly hit problems where if I deleted text while composing an email, "Undo" would not restore it. I filed a bug, which was eventually closed with "we've changed some things around that might have affected this issue, please try to reproduce when the next version is released".
Looking at their issue tracker[1], this kind of thing seems to be a common complaint, rarely resolved with an actual direct bug fix. Most charitably, I assume that Evolution is designed for a use-case or workflow I don't have.
That delete bug doesn't happen for me with current evolution.
The biggest problem I have is the composer window often isn't exactly the same as the sent mail (especially for plain text mail) when it comes to whitespace and quoting. Enabling the Outbox feature is a good workaround as it lets you see the mail before sending it, and you can adjust the mail until it is correct.
Evolution is kind of a web client (like Thunderbird) too, since the message preview pane, including the parts outside the message body, is rendered by WebKit, the HTML for it is generated by evolution. Also the plain text messages go through HTML and WebKit too. Would be nice if these weren't the case though, because they necessarily aren't great for security.
I use bower (fed with isync) in addition to Evolution (because near-instant searching of 15 years of e-mails is rather handy). My coworkers always send email that is readable in a terminal, but apparently customers have this thing called "money" which means they get to dictate whether or not I use HTML e-mail...
I love it. I previously used Sylpheed (and Claws, a fork of Sylpheed), but eventually got to the point where I had to reply to HTML e-mail and that moved me back to Evolution. In addition, its Exchange backend is excellent, which is good because I can't convince O365 to send me calendar invites over IMAP.
