看他们网站上说,会用regular mail寄回.
US Address
To submit by mail or courier, you must include your passport, a copy of the
request letter, and a self-addressed United States Postal Service/ USPS
Express Mail flat rate envelope with the correct postage stamp affixed.
Metered postage is unacceptable.
◦Keep a record of the tracking number on the USPS Express Mail label
so that you can track delivery of the envelope
◦For USPS Priority Mail envelopes, you must also attach a Delivery
Confirmation form with correct postage stamp affixed. Metered postage is
unacceptable.
If you do not provide an acceptable return envelope, the visa office will
mail your passports and original documents via regular mail with no tracking
number.