Generally speaking, applicants are able to use a marriage certificate that was issued in another country if it's an "official" or "certified" copy.
To help determine whether a marriage certificate is official or certified, the U.S. Department of State's "Reciprocity Schedule" provides guidelines from the government agency in each country that issues such documents, as well as whether the certificate should contain any special seals, colors, or formats.
Our comprehensive guide to obtaining a copy of the marriage certificate has more information.
For Boundless customers who have already paid the Boundless fee, their independent immigration attorney will review the marriage certificate to determine whether it meets the government's standards.