What is your anti-virus software on the new PC?

What is your account type on both computers - POP or IMAP?

Old PC using Norton 360, New PC using Microsoft Security Essentials.

OLD PC Server type POP, outgoing is SMTP New PC Server type IMAP, outgoing SMTP

A possible clue - on new PC - it has started working without me changing any settings. What I did on the new PC is notice there is a folder names "Important" and all the many emails in my Inbox were there. I deleted them not from Thunderbird but from the Web Browser Firefox. This I think is what helped all the old emails disappear from my Inbox.

My old PC does not have a folder named "Important".

Recently new messages are appearing in my important folder again though they are no longer in the inbox.

Thanks for any help you can provide on this.

Steve_2pcs said

my pc is dying so I got a newer one and installed Thunderbird on it, using Gmail. My old pc has about 4 messages in the inbox, but on the new pc the inbox has all records received in the last several months. I deleted many of them, but now Thunderbird completely hangs up on the new pc, though it still runs on the old pc when the old pc is able to boot up (not always). I went into the web browser and went to Gmail there, and the inbox also had hundreds of messages, which I deleted all but 5 messages. When I go back into Thunderbird, the inbox still shows hundreds of messages from the past several months, and hangs up (not responding). How do I get it so that when I delete a message from the inbox in Thunderbird on the old pc, it will not reappear in the inbox in Thunderbird on the new pc?

I do not consider this solved. I tried to anwer the question "did this solve it" with a "No" but instead it accepted my last reply as the solution, though it is now

TYPO - last reply should end with "...although it is NOT".

Try to start *Windows* in safe mode with networking enabled.

- Win8 http://windows.microsoft.com/en-US/windows-8/windows-startup-settings-including-safe-mode

- Win7 http://windows.microsoft.com/en-US/windows7/Start-your-computer-in-safe-mode

- XP http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/boot_failsafe.mspx

Still in Windows safe mode, start Thunderbird in safe mode.

- https://support.mozilla.org/en-US/kb/safe-mode

Does the problem go away?

Running Windows in SAFE mode had no effect.

You may consider this problem solved because after I deleted all the messages from the "Important" folder, they stopped appearing.

What still happens is that if I get a new email, read it, and delete on PC number 1, then later if I go into Thunderbird from PC number 2 the new message appears in my box. I can live with this because it is a manageable number of emails I get each day.

Is there some kind of option to synchronize 2 different pcs regarding Thunderbird?

Is there some kind of option to synchronize 2 different pcs regarding Thunderbird?

You'd need to set up your account as IMAP on both computers.