There is an app called tower ghost for Destiny (and many others). You can stay hours and farm in forge. Pick up your engrams, delete the greens. On the app at the top there is a farming application. Press vault and it will suck all your blue engrams to the vault. No need to use postmaster or lose anything. If the vault is full, you can send them to your other characters. You can farm like this for hours upon hours. Then you can reverse this process and when you go to the tower, send them back to your character. Spam the hell out of them and watch all the blues spit out legendary and exotics. Profit.