Does the Certificate of Mailing or Transmission apply to foreign mailings?

The Certificate of Mailing procedure does not apply to papers mailed from a foreign country. However, the Certificate of Transmission procedure can be used for correspondence transmitted to the USPTO from a foreign country, with some conditions. The MPEP states:

The Certificate of Transmission procedure for both facsimile transmissions and transmissions via EFS-Web, however, also applies to papers transmitted to the Office from a foreign country provided that the correspondence being transmitted is not prohibited from being transmitted by facsimile or via EFS-Web and is not otherwise precluded from receiving the benefits under 37 CFR 1.8.

This means that while you can’t use a Certificate of Mailing for papers sent by postal mail from outside the United States, you can use a Certificate of Transmission for faxes or EFS-Web submissions from foreign countries, as long as the specific type of correspondence is eligible for the certificate procedure.