I use the web interface to access my email accounts when I need to clean house.  I've never tried to do it via IMAP but that might be the best option if web access won't work for you.

I'm attempting to go back through a few thousand emails stretching back to 2014.  I wonder if there is a way to save the 'selective mail download' results so that I can work on it over a few sessions.  It takes too long to download the headers each time I want to do some more filtering.

Alternatively, would I be better off using the IMAP connection for this?

Alternative 2: can I set a limit on t he number of headers read, and just work on that subset?

(Before anyone reaches for the flame-throwers:  I have spent a some hours searching through the Help, the PDF manual, and online, but cannot seem to find anything that relates closely enough to my queries - maybe my search techniques are lacking but hope you understand)