Dale Mericle needs to fax, and he’s relied on his Mac since 2000. In macOS Sierra, it no longer works: his USRobotics 5637 doesn’t appear as a printer option. Dale, it’s not you, and it’s not USRobotics, which continues to support this popular USB modem model for dial-up Internet connections, but notes that macOS Sierra doesn’t support faxing.
Apple has a support page updated in September that claims macOS continues to allow direct fax modem support, but folks who rely on faxing have posted reports all over the Internet about how their various USB modems no longer work as a destination for output. Modem makers seem to have confirmed this, though perhaps to avoid annoying Apple, it’s rather tepidly stated on update pages.