收到邮件，大意是：
拿U.S. 10-year B1/B2, B1 or B2 visa的中国公民从November 2016开始需要enroll in Electronic Visa Update System (EVUS)才能进入美国。每次enrollment有效期为两年，两年之后再进入美国之前需要重新enroll。A small fee will be charged to cover the cost of running the system。
U.S. Customs and Border Protection的网站上有更详细的信息。
https://www.cbp.gov/travel/international-visitors/electronic-visa-update-system-evus/frequently-asked-questions