What exactly do you want folks here to do, you deleted your mail and apparently so has google. Did you completely miss the part where is was synchronized.

Normally Gmail deletes mail by placing it is the trash folder and usually unless you empty the trash it remains there. It also remains in the all mail folder. So I think check your google online account for what is in th trash / deleted and the all mail folder.

As you might expect, pop does not behave like imap. Perhaps the "instructions" mislead you, but we cannot offer an opinion on that because you have not cited the web address.

https://support.mozilla.org/en-US/kb/imap-synchronization may be helpful, although it too could be more direct in it's comparison to pop.

I'm not asking for anything. I'm just telling my story.

What exactly do you want folks here to do?

re :I'm not asking for anything. I'm just telling my story.

This Support Forum is for people who require assistance. The people who respond do so in a voluntary capacity in their free time to assist fellow Thunderbird users. They do not appreciate their time being wasted when there is no issue. This Support Forum is not a Chat forum.

If you require assistance then please ask a question and we'll do our best to help, but please do not use this forum as a blog to tell a story.

If you need knowledge to understand what is going on or what settings you need to get a specific result then please ask.

I still use pop for some email addresses and imap for others. So pop is very much alive.

RE POP and lost emails

If you had a pop account and you deleted it because you wanted to create it afresh as an imap account, then it is likely that pop account is still in your profile name folder and so it should be possible to recover those 'lost' emails by getting them back into 'Local Folders' mail account.

That's assuming your old pop account had those emails.

Please state whether this is something you would like to attempt.

Understood. Sorry.

re :I'm not asking for anything. I'm just telling my story. This Support Forum is for people who require assistance. The people who respond do so in a voluntary capacity in their free time to assist fellow Thunderbird users. They do not appreciate their time being wasted when there is no issue. This Support Forum is not a Chat forum.

As you might expect, pop does not behave like imap. Perhaps the "instructions" mislead you, but we cannot offer an opinion on that because you have not cited the web address. https://support.mozilla.org/en-US/kb/imap-synchronization may be helpful, although it too could be more direct in it's comparison to pop.

On this topic there is a plethora of articles

https://support.mozilla.org/en-US/kb/difference-between-imap-and-pop3

https://support.mozilla.org/en-US/kb/switch-pop-imap-account

https://support.mozilla.org/en-US/kb/glossary-terms-including-types-accounts

in addition to https://support.mozilla.org/en-US/kb/imap-synchronization

Thanks for your suggestion. The emails that are saved in Thunderbird are ones which I knew would have lasting relevance; they are in various sub-folders under "Local folders". The rest of the 14,000 I was content to leave on Google's server, for those unanticipated times when I need to look up an old email. I think that I will revert to POP. One never knows when an old email on the Google server might be useful, and IMAP offers no way of doing that, other than blindly saving absolutely everything and cluttering up one's disk space.

RE POP and lost emails Please state whether this is something you would like to attempt.