I had a new Gmail account in September and I wanted to move all mails from my Yahoo mail account to this newly created gmail account.
I used the import mails and contacts option that is built in the Gmail system to move my emails from Yahoo to Gmail. I also enabled the option to forward mails from my yahoo to my gmail for the next 30 days.
It has been 3 months since then yet, email are still being forwarded from my Yahoo account to my Gmail account. I do not require for the mails to be forwarded from my Yahoo to my Gmail anymore.