Nobody sane who cares about keeping emails uses IMAP!
Apart from a few other things (stay tuned) in the IT world, IMAP is a very prominent example of evil.
Many people today claim that nobody uses POP anymore and most email providers nowadays offer access via IMAP. But they couldn’t be further from the truth.
Once you’ve used IMAP and lost (more or less important) emails, you start hating it and might move back to POP.
The basic issue is this: as soon as email clients treat an account as IMAP they are keen on synchronizing, no matter what.
If you’re without internet connection, you might not see any emails (which you had already loaded previously). If you delete emails in one client, it gets deleted on the server (which is the idea) and on all other clients with the same account once they synchronize (which is also the idea).
However, this might not be what the user wants. If I’m without internet connection, I would still like to be able to read previously viewed emails. If I delete emails from one client, it doesn’t necessarily mean I want to consequently delete it on all other clients. Furthermore, once deleted (on the client and hence also on the server) there’s hardly any way to get the email back – same thing applies if you move email inter- and intra-folderwise (and the client and/or server might implement this by deletion). Even if you [accidentally] delete an email on one client and would like to restore it via another client (that had previously loaded the email) which you intentionally unplug from the internet before it could do the sync magic, you might not be successful because the client won’t show you any emails until you synchronize.
Bottom line, if you care about keeping emails (without having to meet extra measures concerning backup) it is not a good idea to use IMAP.
And as a side note: I agree, not all clients follow the above example(s), however most do :).