Long enough to reach you in the U.S. mail. People have been concerned about goods from China, which are safe because it takes longer for them to reach us than the virus can live. However, mail that passes through cities such as New York, or even through the city nearest you that has the virus, can easily be contaminated even if your mail carrier doesn't have the virus. We have to receive our mail, but should always wash our hands or use sanitizer after we handle our incoming mail.