The envelope was not received at the White House, nor did it ever enter the White House. As a matter of practice, the Secret Service does not comment regarding matters of Protective Intelligence. However, in this instance, we can confirm that we are working jointly with our law enforcement partners to fully investigate this matter. Further, all threats directed towards the President, or any Secret Service protectee, are treated seriously and fully investigated.
-- United States Secret Service
Source: U.S. Secret Service