First, tell us exactly what you want to do, as your post is not clear. For example, are you wanting to create a backup of the profile, or are you wanting to extract some messages? With more clarity, I believe we may be able to assist.

I started writing a reply in this topic https://support.mozilla.org/en-US/questions/1453470, but became aware there are four support issues open, almost identical in nature. So chose this topic to reply in and I will close the other. I suggest you note this link to this topic and contain your replies to this topic only. https://support.mozilla.org/en-US/questions/1453447

As you refer to syncing, I assume you have an IMAP account. Archiving in an IMAP Gmail account only works in relation to the gmail all mail folder being the target for the archive action.

Any movement of mail to local folder is done manually and the number involved each time should be limited to only a few hundred email at a time as the more email are selected to move at a time the greater the risk of data loss (emails) in the process.

@David, I am assuming this is letting you know he needed instructions.https://support.mozilla.org/en-US/questions/1453255

I think discussion on this topic https://support.mozilla.org/en-US/questions/1453277 should also be included here as it looks like it is all related to archiving mail from Gmail to a local store.

I have left the other two topics open, but can close them if you like.

Sorry I seem to be making trouble. I still need some help. I assume I can reply to a reply with My Questions. I have learned to archive with Thunderbird open. I want to archive from without the app as was suggested. I don't understand if Thunderbird is to be closed completely or use work offline from file menu. When I am ready to copy emails, where do I select the emails outside the app to copy to external drive & to Local Folders in the profile/mail folder. Thanks.

Is it that we are having a vocabulary problem? That is, my inference is you want to make backups of your messages and remove from the profile. Or do you want to just make backups of selected messages, but not all messages? Instead of discussing mechanics, please just describe what your end goal is. That will help. Thank you. And, you're not making trouble. Most posts require a few interactions to find resolution.

I want to keep all the messages in the profile. I want to copy the older emails to the external drive & to local folders under Profile/Mail folder under users/appdata. Then I want to go to Gmail or Hotmail & delete the older emails from them. That way Gmail & Hotmail will become smaller. Thunderbird will still sync those left & those I add. I will still have the older emails in my profile. I don't know where to select emails to copy to external drive & Local Folders. I assume Thunderbird will still be able to search the older emails in the profile in Local Folders. Do I copy straight from Gmail & Hotmail or where do I select them as Thunderbird will be a closed app? The instruction said to "from here, I suggest exiting thunderbird and copying to external media via windows file explorer and then copy to the Local Folders section of the profile. Let me know if you need instructions." How can I select emails to copy when Thunderbird is closed? I think I am not understanding what it means to archive outside Thunderbird. Thanks. Bottom line is I want to lessen the size of Gmail & Hotmail & still have access to the deleted emails if needed.

Your last sentence is what I wanted: your goal. The easiest way, in my opinion, is to create some folders in Local Folders, and periodically COPY messages there prior to deleting them. Then, delete (move to trash) the messages just copied. That would be my approach as it lets me stay in control. Understand, you need to do periodic backups because if your PC crashes, you lose those messages.