The U.S. Postal Service (USPS) has cracked down on a major distributor of unregulated vapes, blocking it from using its services for business shipments in a significant blow to the multi-billion dollar illicit e-cigarette industry. This action, revealed in letters reviewed by Reuters, stands to benefit large tobacco companies like Altria and British American Tobacco (BAT), which have long battled against the flood of unauthorized vapes, mostly from China.