37 C.F.R. § 7.4
International applications and registrations originating from the USPTO—Requirements to electronically file and communicate with the Office
(a) Unless stated otherwise in this chapter, all correspondence filed with the USPTO relating to international applications and registrations originating from the USPTO must be submitted through the trademark electronic filing system and include a valid email address for correspondence.
(b) Applicants and registrants under this section must provide and maintain a valid email address for correspondence with the Office.
(c) If an applicant or registrant under this section is a national of a country that has acceded to the Trademark Law Treaty, but not to the Singapore Treaty on the Law of Trademarks, the requirements of paragraphs (a) and (b) of this section do not apply.
(d) If the trademark electronic filing system is unavailable, or in an extraordinary situation, an applicant or registrant under this section who is required to file a submission through the trademark electronic filing system may submit a petition to the Director under § 2.146(a)(5) and (c) of this chapter to accept the submission filed on paper.