Normally, I carry packages to the Post Office on my full-sized bikes. Through some recent experimentation, I have come to the conclusion that, for packages less than 15 pounds, Brahma is definitely a viable option.
Carrying a USPS Large Priority Mail box on the rear rack of Brahma is not at all difficult. However, it took me a while to figure out where to place my feet on the pedal, so that they didn't rub on the package on the rear carrier rack.
The other nicety is that I can take Brahma (with the packages on the bike) into the Post Office with me. I like it!