Linker error for vcpkg built package

[Perdrix]

I'm getting the following linker errors:

1>SmtpMime.lib(mimecontentformatter.cpp.obj) : error LNK2001: unresolved external symbol __imp_qt_version_tag_6_9
1>SmtpMime.lib(mimecontentencoder.cpp.obj) : error LNK2001: unresolved external symbol __imp_qt_version_tag_6_9
1>SmtpMime.lib(mimebase64formatter.cpp.obj) : error LNK2001: unresolved external symbol __imp_qt_version_tag_6_9
1>SmtpMime.lib(mimeqpformatter.cpp.obj) : error LNK2001: unresolved external symbol __imp_qt_version_tag_6_9
1>SmtpMime.lib(mimebase64encoder.cpp.obj) : error LNK2001: unresolved external symbol __imp_qt_version_tag_6_9
1>SmtpMime.lib(mimeqpencoder.cpp.obj) : error LNK2001: unresolved external symbol __imp_qt_version_tag_6_9
1>SmtpMime.lib(mimepart.cpp.obj) : error LNK2001: unresolved external symbol __imp_qt_version_tag_6_9
1>SmtpMime.lib(quotedprintable.cpp.obj) : error LNK2001: unresolved external symbol __imp_qt_version_tag_6_9
1>SmtpMime.lib(mimemultipart.cpp.obj) : error LNK2001: unresolved external symbol __imp_qt_version_tag_6_9
1>SmtpMime.lib(mocs_compilation.cpp.obj) : error LNK2001: unresolved external symbol __imp_qt_version_tag_6_9
1>SmtpMime.lib(emailaddress.cpp.obj) : error LNK2001: unresolved external symbol __imp_qt_version_tag_6_9
1>SmtpMime.lib(mimemessage.cpp.obj) : error LNK2001: unresolved external symbol __imp_qt_version_tag_6_9
1>SmtpMime.lib(smtpclient.cpp.obj) : error LNK2001: unresolved external symbol __imp_qt_version_tag_6_9
1>SmtpMime.lib(mimetext.cpp.obj) : error LNK2001: unresolved external symbol __imp_qt_version_tag_6_9
1>SmtpMime.lib(smtpclient.cpp.obj) : error LNK2019: unresolved external symbol "__declspec(dllimport) public: char const * __cdecl QMetaEnum::valueToKey(unsigned __int64)const " (__imp_?valueToKey@QMetaEnum@@QEBAPEBD_K@Z) referenced in function "protected: void __cdecl SmtpClient::changeState(enum SmtpClient::ClientState)" (?changeState@SmtpClient@@IEAAXW4ClientState@1@@Z)
1>SmtpMime.lib(mocs_compilation.cpp.obj) : error LNK2019: unresolved external symbol "__declspec(dllimport) public: struct QMetaObject const * __cdecl QObjectData::dynamicMetaObject(void)const " (__imp_?dynamicMetaObject@QObjectData@@QEBAPEBUQMetaObject@@XZ) referenced in function "public: virtual struct QMetaObject const * __cdecl MimeContentFormatter::metaObject(void)const " (?metaObject@MimeContentFormatter@@UEBAPEBUQMetaObject@@XZ)
1>  Hint on symbols that are defined and could potentially match:
1>    "__declspec(dllimport) public: struct QMetaObject * __cdecl QObjectData::dynamicMetaObject(void)const " (__imp_?dynamicMetaObject@QObjectData@@QEBAPEAUQMetaObject@@XZ)
1>D:\Github\DSS\x64\Debug\DeepSkyStackerLive.exe : fatal error LNK1120: 3 unresolved externals

the portfile.cmake looks like:

vcpkg_check_linkage(ONLY_STATIC_LIBRARY)

vcpkg_from_github(
    OUT_SOURCE_PATH SOURCE_PATH
    REPO deepskystacker/SmtpClient-for-Qt
	REF 79eb946c5be718149847ea0bd015a3cebcbf9f98
    SHA512 00f3e14dd649d46a878b06f9c4a525907fa8f3072d58fc7bcb9e8a3a73c0289049e54c4170f8d024d1c001928e4af7d66a391e297be0b6a9f3cf07bc6ff2f16d
    HEAD_REF V2.0
	
)
set(ENV{QT_DIR} $ENV{QTDIR})
set(ENV{Qt6_DIR} $ENV{QTDIR})
set(CMAKE_AUTOMOC ON)

set (options
	"-DBUILD_SHARED_LIBS=OFF "
	"-DBUILD_DEMOS=OFF "
	"-DBUILD_TESTS=OFF "
)

message ("****************************************************************")
message ("Setting build options: " ${options})
message ("****************************************************************")

vcpkg_cmake_configure(
    SOURCE_PATH "${SOURCE_PATH}"
	OPTIONS ${options}
)

vcpkg_cmake_install()

vcpkg_copy_pdbs()

vcpkg_fixup_pkgconfig()

vcpkg_cmake_config_fixup(CONFIG_PATH "lib/cmake/${PORT}") 

file(REMOVE_RECURSE "${CURRENT_PACKAGES_DIR}/debug/include")

file(INSTALL "${CMAKE_CURRENT_LIST_DIR}/usage" DESTINATION "${CURRENT_PACKAGES_DIR}/share/${PORT}")
vcpkg_install_copyright(FILE_LIST "${SOURCE_PATH}/LICENSE")

what am I doing wrong please?

Even stranger - this only happens with an MSBuild build. The CMake build works fine.