client/lib/domains/email-forwarding/index.js
function getEmailForwardingSupportedDomains( domains ) {
	return domains.filter( function( domain ) {
		const domainHasGSuite = hasGSuite( domain );
		const wpcomHosted =
			includes( [ domainTypes.REGISTERED ], domain.type ) && domain.hasWpcomNameservers;
		const mapped = includes( [ domainTypes.MAPPED ], domain.type );
		return ( wpcomHosted || mapped ) && ! domainHasGSuite;
	} );
}
function getEmailForwardingSupportedDomains( domains ) {
	return domains.filter( function( domain ) {
		const domainHasGSuite = hasGSuite( domain );
		const wpcomHosted =
			includes( [ domainTypes.REGISTERED ], domain.type ) && domain.hasWpcomNameservers;
		const mapped = includes( [ domainTypes.MAPPED ], domain.type );
		return ( wpcomHosted || mapped ) && ! domainHasGSuite;
	} );
}
Filters a list of domains by the domains that eligible for Email Forwarding

@param {Array} domains - list of domain objects
@returns {Array} - Array of Email Forwarding supported domans