I guess I tend to use email in a non-standard way. I provide a general email address (for friends and family) and have it forwarded to my ISP. Typically when I send mail its specified as my public email address such as it doesn't confuse people, the default email client doesn't support that (not using IMAP at least). That would be a feature that is nice to have.
I've relied on K-9 to bring a consistent IMAP email experience to the variety of Android phones on the networks that I manage. Its great to sidestep the variety of flavors of Android and different manufacturer interfaces. Kaiten, their tablet version has the same great features and uses the tablet screen space to its advantage.
I found K-9 mail to work great because of the IMAP setting and folder capabilities (I did not even know about this IMAP ability till reading this thread. One crucial thing that K-9 lacks though, is search capabilities. Although that seems to be a problem with all Android mail apps.
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