You have to split your MBOX file of thunderbird because it has grown too large. There can be several ways to split MBOX file into smaller files, we can either use Thunderbird email client, where we by creating a new folder under the local folder, can move our data from the heavy folder to the newly created folder. Splitting the data into 2 folders:
1st, the original folder, which was heavy
2nd one, which was newly created.
But there are limitations, like if the files are too heavy, the system can hang, lag, or even shut down, plus we have to move individual files from each mailbox, and if you have many inboxes. It becomes time-consuming and effort-taking to split them.
Therefore, other solutions include using an expert MBOX splitter utility like BitRecover MBOX splitter, which eliminates the problem of bulk transfer, where you can import multiple files and split them accordingly. The data can be split according to subject, date, and you can also select the size at which you want to split your files. The tool works by opening an important folder or file in the tool using the open option.