Go look at the Server settings under the yahoo account you setup in TB;
there's a checkbox to leave messages on the server. Another checkbox to
delete them from the server when you delete them in TB, which is what I
use, otherwise, I end up having to go into Yahoo mail on the web and
delete them a 2nd time.
As for putting your emails back into yahoo's Inbox, you have to email
them back to yourself. The easiest way so that they don't all come back
in as Forwards, is to use the Redirect plugin for TB.
Mail Redirect add-on for TB:
https://addons.mozilla.org/en-US/thunderbird/addon/550
IMPORTANT! To install the Mail Redirect Add-on:
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1. Make sure you Right-Click on the [Download Now] button and Save Link
As... (to your Desktop or anywhere you'll remember).
2. Run TB.
a. Open the Tools menu, Add-ons...,
click on the Extensions tab, and click on the [Install...] button
b. Navigate the
File:Open... window that pops-up; go to your Desktop
and select the mail-redirect<version>.xpi
you downloaded
c. Click Open, the window will close and and an Install Add-on window
will popup.
d. Click on [Install Now].
3. After installing the add-on, you should be prompted to click a
button Restart Thunderbird;
if not, close TB and restart it yourself to complete the
installation of the add-on.
After installing the add-on, select a message (to test it out the
add-on).
To demonstrate this add-on, I used it to redirect a copy of your email
back to you.
Notice how it shows up? It doesn't come embedded like a Forwarded
email!!
ENJOY!
John