Deal With Oversized MBOX File Issue

1. Delete unnecessary emails and compact folders It is the first step anyone could think to create some free space. Look over your mailbox to find out the emails that are not required, and delete them. However, in many MBOX email clients, the folders need to be compacted so as to reclaim the space created by the deletion of items as this is not done automatically.
2. Split MBOX File using a Text Editor Splitting your MBOX files using a text editor could be a great way to reduce mailbox size. You can use any text editor including Notepad++, JujuEdit, EditPad Pro, EditPad Lite, EmEditor, HiEditor, HxD, ifhex, HexFiend, UltraEdit, VEDIT, VEDIT Pro64, and Vim for this. Make sure you check the platform compatibility to run these editors on your system. Once you have installed the text editor of your choice, follow the given order of steps:
   1. Create two extra copies of the mbox file.
   2. Open one of those copies with the text editor.
   3. Click anywhere in the middle of the file. Search for the header named as Message ID. It contains a unique value for every mail.
      [Note: You can copy that ID separately to notepad or notes for reference]
   4. Scroll to the end of the message. Delete entire message below that point and save the file.
   5. Open the other copy of your file. Find the unique Message ID from where you split.
   6. Then, delete all the messages above that Message ID and save it.

MBOX users can choose different ways reduce the size of their MBOX files. As the first method, they can delete the unwanted emails and then compact the folders. Alternately, they can split the MBOX file manually using a text editor.