if you would like to continue accessing account online, go with IMAP setup. The messages stay on server and copies on PC. But don't be fooled; if you delete what you see on PC, the version on server is also deleted. This is preferred approach, as you can then access messages from other pcs, the web, or phone. and the version on PC can be exported to other formats.

Here is the crux of my problem. My ISP imposes a 150 MB limit on back e-mails, and it is hard to keep the account from filling up. I need to get the excess off the server and into storage that I can manage and copy to files I can find again (usually categorized by the name of the correspondent on the other end). Does Thunderbird allow this?

Here is the crux of my problem. My ISP imposes a 150 MB limit on back e-mails, and it is hard to keep the account from filling up. I need to get the excess off the server and into storage that I can manage and copy to files I can find again (usually categorized by the name of the correspondent on the other end). Does Thunderbird allow this?

It can be done, but you are making hard work out of something that should be simple.

Lets start at the beginning. Are you dedicated to using this web interface to access your account, or can you do everything you need with your emails from within Thunderbird?

If yes, just use Thunderbird and move whatever emails you want to local folders (the account named as such in Thunderbird) on a daily/weekly basis and they will be stored as emails on your local PC, no searching for files on your hard disk stored using arcane file names only you understand and can sometimes remember, just another folder of emails in your Thunderbird program. No different to your imap account email in Thunderbird, but no longer on your providers mail server.

As long as your mail provider is not using googles gmail as a backend, you can also use the archive feature in Thunderbird to point any archived mail to the archive folder on local folders where they can be stored in yearly groups in their original folder names (they are created as needed automatically)

So I would recommend a combination of archiving with manual mail moving to get almost everything off the mail server and store is locally in Thunderbird.

Alternatively you could create a POP account in Thunderbird which will download everything in the inbox on the server, and optionally immediately or later delete it from the server (there are retention on server settings in account settings). The result is a local only copy of mails which are stored only locally and your server account will be emptied on each download. No muss no fuss.

The subset is the problem in this ointment, as until the mail is downloaded Thunderbird has no idea what subsets you might even have to try and define. It is a but like saying words beginning with Q is a subset of the contents of a dictionary. You have no idea what the quantum of that is until you actually open the dictionary and read it. Hence mail clients mostly work on get it all or get nothing principals.

Yes, it might be possible for me to get by using Thunderbird alone, if I can get it to perform some related tasks. I will post that as a separate topic