How does inmate know that I put money on his comissary

I live in Texas, mu brother is in Fulton, Mo (FDOC). I sent him a letter via email a as soon as he was transferred there which has only been a week and a half. Will he know to go to computer to check for emails? He is not very computer literate and he doesn't expect any mail from anyone. Do they automatically set up an account to receive letters via email?? I sent him a letter through regular snail mail today to let him know that I have been sending letters on the computer but he is only in there for a few more weeks before he gets transferred to a rehab facility I am just hoping he gets the letters I sent email. I know it costs money to send but I also put money on his commissary. Do I need to put money on the "wallet" on this website for him as well or can he use the commissary to write a letter to me on computer? Thank you SO much for your time and help. -by Mandy M.