This is not a thunderbird shortfall; you have an immense amount of mail. If this is IMAP (which I infer it is) and there are thousands of folders, this places a huge demand on your internet connection. Assuming all folders are set for offline use (settings>synchronization&settings - advanced button), I suggest clicking file>offline>download to retrieve them and, after the download, export to PC files so future searches will go much faster.

Thank you so much for replying.

Yes, my dad has an immense amount of mail and a crazy number of folders and I am not surprised it may cause issues.

He's over-organized, for sure. There's a long backstory with how his Outlook got screwed up and I'm trying to make things better for him. He doesn't like the Gmail interface, and it seems Thunderbird can handle large email accounts better than Outlook, which keeps having issues, so I'm giving it a try.

Would Thunderbird eventually download everything on it's own via the scheduled "Check for new messages" setting?

It downloaded a very large number to begin with that took a long time (as expected), so I thought it might just continue doing that until everything had been downloaded), but alas, not so.

It is IMAP, yes.

I checked Settings > Synchronization & Storage > Advanced settings and yes, all folders were already set for offline use.

How do I go File > Offline > Download? Using Thunderbird 128.0.1esr (64-bit) on Windows 11.

if the menu bar is not shown, click the alt key. Then, the file option in number is shown. My suggestion to you is to also set view>toolbars and tick menu bar so that it is always visible.

On your other question, I do not know if thunderbird will keep chugging along for thousands of folders, but it may.

Thanks! I tried File > Offline > Download/Sync now > OK (Mail Messages was ticked for download, nothing else) but I am getting this error message coming up for each folder:

"The operation failed because another operation is using the folder. Please wait for that operation to finish and then try again."

Any thoughts?

I quit Thunderbird, re-started it, and did the File > Offline > Download/sync now, but this time I clicked on "Select" and un-ticked all the folders it had already downloaded emails for.

It then began, at the very bottom of the window, rapidly flashing "Opening folder [Folder name]" "Downloading message header X of Y," and "Downloading message" and folders that previously had not emails are now getting populated with emails.

It is also still, for some folders, displaying the warning "The operation failed because another operation is using the folder. Please wait for that operation to finish and then try again."

Even if some folders don't get their emails downloaded, it should be a smaller number I have to manually click on.

Thanks so very much!

I found a Reddit post about the warning "The operation failed because another operation is using the folder. Please wait for that operation to finish and then try again" and read that I should try turning off the Setting "Compact all folder when it will save over X MB in total" and the warnings stopped :)

You appear to making trouble for yourself.

Compacting only occurs when mail is deleted from a folder. Disabling and re-enabling sync on the folder via subscribe will de exactly that. The server will notify Thunderbird it's image is out of date, everything will be deleted and it will start the download over again.

Your issue is most likely you have exceeded the allowance of data (bandwidth) google allow for an individual for the day. See https://support.google.com/a/answer/1071518?hl=en

With a store of gigabytes it may take a week or more to fully sync, and if you have an antivirus scanning in the profile folder or scanning the encrypted communications months, if ever, gets closer to it. Essentially the sync can be interrupted and timeout and this gets much worse when something else is probing the connection (antivirus) it will start over after a timeout, and for downloads will eventually get there after lots of restarts of the process and lots of deletions of what has already been downloaded because the last attempt failed , but I don't recommend email scanning at this time to either the profile folder or email downloads generally.

I would also suggest, initially in this case as least, that you use the settings in Thunderbirds account settings to not store emails on the local system. This will mean that Thunderbird will download just enough information to populate the lists in the user interface but not all the mail bodies, they will be downloaded on demand when a message is selected to be read. This will greatly reduce the bandwidth needed to establish the account. If after you have folders that look like they have the mail in them you could set it to download mail locally if you like, but lots of people never store IMAP mail locally. It is certainly not a local backup even when they do as it can be deleted simply be the server being uncontactable.

I read that the process of compacting folders interferes with the Offline --> Download/Sync Now process, and once I turned off "Compact all folders when it will save over 20 MB" indeed the error messages stopped.

After that, Thunderbird kept on downloading emails, so I cannot have exceeded the daily Google bandwidth.

"You appear to be making trouble for yourself" is also a rude, know-it-all tone to take.

We're all doing our best in this life, dude! Be kind, okay?

well explained by Matt!!! i think its gonna be easy for Rob to sort out now!!! just crazy to know why big boss receive thousand emails.