Will Migration Assistant transfer just mail?

I have an iMac and just bought a MacBook Air. I want to transfer just my Mail and all its folders over to the MacBook. Can I do this or will the Migration Assistant make me transfer all my other files?

Also, once I have Mail on both Macs, will my new emails appear on both? Is there a setting I need to apply to do this? I use Gmail and Yahoo.

Thanks,

Sunny