Restoring from TM backup causes Mail to import and eat up HD space on Mac Air I use a MacBook Air 256 GB HD on Yosemite 10.10. I recently noticed large date range of emails gone missing. Rebuilding the mailbox did not solve the problem so I decided to restore my entire Mac from the Time machine. 5 days of frustration and here I am.

Time Machine restores from the backup however, when I start Mac Mail, it starts to import the messages. I have 130 GB of emails. It seems what happens is when Mail is importing the messages, it is creating a duplicate folder in the system and that is eating into the HD space and not allowing the system to restore as it runs out of space. By the time it has imported nearly all the emails, my mac has run out of space and hence does not allow me to return to the original state. 

Any reason why this duplication of emails and even if so, where are these duplicate emails stored so I can manually delete that folder?
I would try in ~/Library/Mail. You can delete the contents in this folder, then go into mail and rebuilt your inbox to make sure everything syncs.

Note: it's called the MacBook Air