Changing the Mozilla Thunderbird settings
To leave messages on the server, you will:
Open the server settings window for your mail account
Check the Leave messages on server checkbox
1. Start the Mozilla Thunderbird program.
When Thunderbird opens, click Tools, then Account Settings from the menu bar.
2. The Account Settings window will appear.
Click the small "plus sign" to the left of the account to expand the list beneath it.
Click Server Settings.
Check the box next to Leave messages on server. Untick the Until I delete or move them from Inbox and For at most X days.
3. Close the Account Settings window.
Click OK to close the Account Settings window.
Trouble logging in? Simply enter your email address OR username in order to reset your password.
For faster and more reliable delivery, add firstname.lastname@example.org to your trusted senders list in your email software.