Sample code excellently explained by Jetbrains AI Assistant: externalemailprovider

externalemailprovider.cpp

// Provides the interface for plugging in a new external email provider.
export class ExternalEmailProvider {
 public:
  // Provides the contract for sending an email through the external email
  // provider.
  virtual auto sendEmail(Email&& email) -> async::NoneAsync = 0;

  // Provides the contract for diagnosing the external email provider.
  virtual auto diagnose(
    proto::EmailProviderDiagnosisActionType_Enum action,
    ExternalEmailProviderDiagnosisContext&& ctx)
    -> async::coroutine<proto::EmailProviderDiagnosisResponse> = 0;
};