diff --git a/agents/unifiedmailboxagent/CMakeLists.txt b/agents/unifiedmailboxagent/CMakeLists.txt
--- a/agents/unifiedmailboxagent/CMakeLists.txt
+++ b/agents/unifiedmailboxagent/CMakeLists.txt
@@ -1,6 +1,6 @@
 add_definitions(-DTRANSLATION_DOMAIN=\"akonadi_unifiedmailbox_agent\")
 
-set(CMAKE_CXX_STANDARD 14)
+set(CMAKE_CXX_STANDARD 17)
 
 if(BUILD_TESTING)
     add_subdirectory(autotests)
diff --git a/agents/unifiedmailboxagent/utils.h b/agents/unifiedmailboxagent/utils.h
--- a/agents/unifiedmailboxagent/utils.h
+++ b/agents/unifiedmailboxagent/utils.h
@@ -24,12 +24,20 @@
 #include <QHash>
 #include <QString>
 
+#if __has_include(<optional>)
+#include <optional>
+namespace stdx {
+using namespace ::std;
+}
+#else
 #include <experimental/optional>
 namespace stdx {
 // Injects content of std::experimental namespace into "exp" namespace.
 // C++ is magical.
-using namespace std::experimental;
+using namespace ::std;
+using namespace ::std::experimental;
 }
+#endif
 
 template<typename T>
 inline QList<T> setToList(QSet<T> &&set)