I just need to stop the server from deleting them on my local machine when I delete them on the server (gmail).

You can't, if your account is IMAP. This is just how IMAP works. To free up space on the server you'd have to move messages off of the server to your Local Folders account. Note, don't attempt any mass transactions, i.e. don't try to move everything at once. Start with a single message, and then continue with smaller batches. The server may limit the no. of messages you can transfer within a certain amount of time.

Hi christ1, Thanks for your prompt reply! I tried to select all my emails in my account (ctrl a) but this apparently caused Thunderbird to freeze. I had wanted to copy all of them to a local archive folder. I think there are a total of about 174 thousand emails I'd like to archive. Moving them by chunks will likely take hours. I don't mind if it takes hours or days of computer time but I don't want to spend hours or days of my time doing it manually. Is there any better way to handle this automatically? What if I switch to POP? Thanks, Phil

Is there any better way to handle this automatically?

I don't think so. You could buy more storage space from Google though.

What if I switch to POP?

And what would be different with POP? You'd still have to deal with all the messages currently stored on the server.

Wouldnt it work to change your "Archive" destination to "Local Folders", then just highlight emails to be archived, right click, and select Archive? I had quite a few as well and had to do them in batches of around 2,000 each. I still need to confirm they are actually local and no longer on my email server (which if you'd like to ditch gmail all together, I can help!) It'd give you greater control of your emails and allow you to 'FTP' them all over to a local drive since you have so many. -Steve