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As clients, I use K-9 on Android and Apple Mail or runbox7 on the desktop. Outside of work, I have the same setup with Apple Mail and Spotlight for archival and search. In my experience, it works well and doesn't feel significantly slower than searching locally in my offline archive. However, if I'm already working in OWA, I use the search function in there.
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I never use the app itself but frequently use Spotlight to search for and preview e-mails. To have an offline archive, I also have Apple Mail connected to my Exchange accounts. However, in the end I don't care all that much about my e-mail client because I use a simple inbox-zero-ish approach to e-mail and only really need Inbox and Archive folders (as well as a delete function). Sometimes, I need to reach for the desktop version of Outlook in a Windows VM to access options or features not accessible in OWA (or in the sluggish abomination that is Outlook for Mac). It's simple, feels reasonably snappy to me and I like having the same interface on all the different machines I need to login from. As a client, I use Outlook Web Access (OWA) most of the time and I think it's fine. I've only ever worked at places with self hosted Exchange for e-mail and groupware.
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