CMake Warning:
  Manually-specified variables were not used by the project:

    CMAKE_EXPORT_NO_PACKAGE_REGISTRY
    CMAKE_INSTALL_DATAROOTDIR
    CMAKE_INSTALL_LIBEXECDIR
    CMAKE_INSTALL_OLDINCLUDEDIR
    CMAKE_INSTALL_SBINDIR


In file included from /home/conan/w/cci_PR-4017/.conan/data/mailio/0.20.0/_/_/build/1bc89d58dfa58c7e8e085b24fd8d376db20d846a/source_subfolder/src/imap.cpp:27:
/home/conan/w/cci_PR-4017/.conan/data/mailio/0.20.0/_/_/build/1bc89d58dfa58c7e8e085b24fd8d376db20d846a/source_subfolder/include/mailio/imap.hpp:19:10: fatal error: 'optional' file not found
#include <optional>
         ^~~~~~~~~~
1 error generated.
make[2]: *** [source_subfolder/CMakeFiles/mailio.dir/src/imap.cpp.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [source_subfolder/CMakeFiles/mailio.dir/all] Error 2
make: *** [all] Error 2
mailio/0.20.0: WARN: Build folder is dirty, removing it: /home/conan/w/cci_PR-4017/.conan/data/mailio/0.20.0/_/_/build/1bc89d58dfa58c7e8e085b24fd8d376db20d846a
mailio/0.20.0: ERROR: Package '1bc89d58dfa58c7e8e085b24fd8d376db20d846a' build failed
mailio/0.20.0: WARN: Build folder /home/conan/w/cci_PR-4017/.conan/data/mailio/0.20.0/_/_/build/1bc89d58dfa58c7e8e085b24fd8d376db20d846a
ERROR: mailio/0.20.0: Error in build() method, line 68
	cmake.build()
	ConanException: Error 2 while executing cmake --build '/home/conan/w/cci_PR-4017/.conan/data/mailio/0.20.0/_/_/build/1bc89d58dfa58c7e8e085b24fd8d376db20d846a/build_subfolder' '--' '-j3'