Can the U.S. Postal Service – the micromanaged “economic Frankenstein” that it is – do anything for startups? For one mobile fashion upstart, it may actually be a game changer. That’s because Poshmark, a site where women create virtual closets via their mobile phones to sell their clothes and shop other women’s closets, has teamed up with the Postal Service to bring users PoshPost, a USPS shipping label designed specifically for fashion items.