you could prolly do it with salesman. just dont have it listing any items for sale. it will check for auctions (obviously none there) then goes to mailbox. deposits items. then withdraws shit to sell (obviously nothing to withdraw). then it will wait x amount of time and repeat the process.
should work a treat.
mine does something similar as wellsalesman is the worst shit ever happened to this world. it will just check once in mailbox (just 50 mails) and then sits afk...so bad. if i had 20 euros to spend, i would rather f**k a prost**ute with Aids