Hi - I "think" you are starting to get into the fundamental difference between POP and IMAP email. Not an expert here at all, just a poking beginner.

My limited understanding of IMAP is that unlike POP, it tries to be synchronized with actions on the email client (s). These clients can be "on line" or "off line and synchronized later".

The advantage of this is that it allows you to more easily use multiple computers / devices / web mail to capture all of the emails. (which is what I really do, so I use IMAP instead of POP) Actual detailed use gets trickier.

Once you tell the IMAP email software that you have "read" a file, it no longer is "unread", so the envelope will show it as "open". I don't know how to change this back to an "un open email" in IMAP, but it might be possible in a POP format. The problem, is that to do this in POP, it will assume that nothing has been read. (I think)

If you delete an email in IMAP, it becomes less clear, as you appear to have the option both in your client(s) and your email server setup to either retain or delete emails that are opened / deleted, both at the client level and the server level.

I have largely given up trying to delete emails using this client, as I just could not figure out what it was doing in relation to the server, and frankly, it was too slow. I also have not been able to get it to recognize the IMAP folders which I know are on the system. I use my desktop Opera browser / client or web mail to do the heavy lifting, and just keep the 770 client fully sync'ed with both the headers and contents (but not attachments). This goes pretty fast.

Last but not least, I have read that very few server / client software programs are actually fully compliant to IMAP, so that can be a factor as well.

Sorry if that is not really an answer. I actually have posted in the Opera forum requesting that they port their email client over to the 770 - who knows ?