All gmail emails were downloaded to local computer via Thunderbird.

It is expected that all emails downloaded to local computer via Thunderbird should be visible even after they are deleted from main gmail account. </blockquote> That will only be the case if you download using pop. IMAP is synchronised.

However, the emails that were previously downloaded by Thunderbird to local computer are no longer accessible/available for viewing after they were deleted from the main gmail account?

Sounds like you accepted the default recommendation and added your account as IMAP. So you have deleted your email.

It also sounds like you were trying to do some sort of archiving, which you should have done using Google takeout See https://takeout.google.com/ Faster, cleaner and more accurate as Google hand off your mail as a series of discrete mbox files one for each label which Thunderbird can read, or which can be imported with an addon. https://addons.thunderbird.net/en-US/thunderbird/addon/importexporttools-ng/?src=ss

Hi, Matt.

"That will only be the case if you download using pop. IMAP is synchronised."

"Sounds like you accepted the default recommendation and added your account as IMAP. So you have deleted your email."

Yes, via IMAP my emails were deleted.

"It also sounds like you were trying to do some sort of archiving, which you should have done using Google takeout See https://takeout.google.com/ Faster, cleaner and more accurate as Google hand off your mail as a series of discrete mbox files one for each label which Thunderbird can read, or which can be imported with an addon. https://addons.thunderbird.net/en-US/thunderbird/addon/importexporttools-ng/?src=ss "

Thankfully, I did do a Google Takeout download prior to installing Thunderbird. Thank you, Matt, for the information on using POP and the link for importing instructions of the mbox file. Thank you very much once again.