You shouldn't be hitting a limit.

But you also don't say what you are seeing (or not seeing) that indicates something is wrong.

But even before going there, if you have an mbox file, containing a folder of messages, you want the file name to NOT have a file extension under Local Folders.

(Please post your responses here, not in private messages.)

> i don't fully understand what you mean

Your screen shot shows folder names of

 All Mail xxxxxx.mbox

You should remove .mbox from the file name

Also, where did the files come from, what email client, and what operating system?

The file name was given by the Google (See attached Photos)

We have our gmail account, but we will shutdown our account. So from their, we have ask the google support and we have downloaded this files..

Using Thunderbird we want to import the mbox files so that we can still access to the email.

We have tried few mbox file (Marie, Dan, Theresa) and it was successful. But the All mail xxx -006 and All mail xxx-03 was unsuccessful (Shown on the 1st photo above).

While there is probably no limit, there is probably a functional limit of the system ram. Not the virtual memory which would see Thunderbird slow to the point of appearing frozen, but real ram. You might be looking at needing server sized memory modules. But I would think you would need more that the Windows 10 home limit of 128Gb

Then we have the very real issue of disc access times. The mbox file must be read to create the MSF file that is used to populate the user interface with list of mail etc.

Given access can usually be considered to take 10 minutes per GB I would expect it to take perhaps an hour just to generate the relevant index. Bot through any slowness of Thunderbird per sae but due to the limitation of reading data off the physical disk.

Then their is the issue of the secondary process that generates the global index. How large is the global-messages-db.sqlite file in your profile folder? My guess is huge.

I would suggest breaking the files into manageable chunks. I doubt you have enough hardware to ever open the mbox files in Thunderbird as they are. Mbox files are text files, so chopping them to size using a text editor is possible, but it will be slow.

There are some text editors that can open GB sized text files linked to and discussed here https://www.ghacks.net/2018/02/22/how-to-open-gigabyte-sized-text-files-on-windows/

Having said all that, I don't think your import has failed. It is just still being indexed is my uninformed guess and that might or might not ever complete.

Some good points by Matt.

You might try a) disabling indexing at tools > options > advanced > general > uncheck "Enable global..." b) 64bit build from https://releases.mozilla.org/pub/thunderbird/releases/60.5.1/win64/en-US/Thunderbird%20Setup%2060.5.1.exe

You have a beefy computer? With how much memory? (hopefully more than 8gb)