There are 3 (well, 2 + infinite) email protocols - POP3 is the oldest one. Emails are kept on the server. Delete one and it's gone. Then came IMAP. Emails are kept in the email program. Delete one and it's gone in that program, but if you use an email program on your desktop, on in your laptop and an app in your phone, deleting it on one won't delete it on the others.
Then there's Exchange. That's Microsoft's email server. It doesn't use POP3, it doesn't use IMAP, it uses its own proprietary protocol (as does just about everything Microsoft makes). You need a different email app to access that and, so far, a lot of people have written a lot of apps for it, some of which have worked pretty well, some of which hardly worked. It seems that Google has added an Exchange API to the suite of email APIs in Android.
(The reason I said infinite is that you can set Exchange Server up to do almost anything, so any administrator can break the ability of any program to access an Exchange server - even the full version of Outlook running in Windows. Following the manual works, but some companies want to change little things, so you can never tell if an Exchange [or Outlook] app that's been working will continue to work if someone makes a change at the server.)
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