Do you have only Mining and Herbing bags equipped in your 4 bag slots? Mailing never sends anything in your backpack and does not recognize the "special" mining and herb bags as having free slots. So if you are using 4 special bags and they get full along with your backpack, the backpack will never empty after mailing and your bot will show zero bag space available, even if the "special" bags are empty. The bot will go into an endless loop after that because it thinks all your bags are full. Make sure to have at least 1 regular bag in use besides the backpack. At least that is how it used to be. Not sure how it is after the last few updates.