Pjiang or other friends:
1). Should I use street address (USCIS, 850 S ST, Lincoin, NE 68508-1225) for mailing NIW I140 REF? I can ship to this address by USPS as you suggested in your article.
2). or should I use the mailing address (it's P.O. BOX #) on the enclosed envelop? If so, I need to mail my REF using UPS or Fedex (not USPS).
Please give me suggestions,
Thank you,