Hi Rose,

First, you'll want to make a back-up copy of your data and store it on an external drive. It's best to back-up your whole hard drive occasionally. Maybe you are doing this already. For now, you could also just make a copy of your Thunderbird profile. To find your profile folder, click on the Help menu > Troubleshooting information > look for "Profile Folder" in the left column of the Application Basic table, and click on "Show in [...]" next to it.

(You could export your messages from Thunderbird, which is easier than copying your profile folder, but, if you have so many messages that you have reached the limit on the server, you may also have too many messages to export.)

Now, your question.

If your account is an IMAP account and your messages are in IMAP folders, whatever you do in Thunderbird or on the server will be reflected in the other location. Deleting messages in one place will delete them everywhere. If it's easier to delete them in Thunderbird than on the server, you can do that and never deal with webmail.

But before that, you have to preserve your messages in Thunderbird. You do that by creating local folders and copying the messages to the local folders.

If your account is a POP account, messages are not sychronized, so deleting them at the server will not delete them from Thunderbird.

If you do not know your account type, click on the name of the account in the folder pane. Select "Settings" from the drop-down menu. Click on "Server Settings" on the left, and look at the top right for server type.

If you need guidance with any step, please ask.

Thank you for the quick response. It is very much appreciated.