Last week I searched for an email in Mail.app. It was right there on the screen and it couldn’t find it. It also fails to display or even list some attachments.
This is unacceptable to me. Yet I keep using it because I dislike Gmail’s web interface and my Vim imap setup is not really usable yet and probably never will be.
Outlook has the same searching issue. I often have to resort to manually eyeballing through my email archives to find what I'm looking for. Very annoying indeed.