/usr/include/KF5/MailCommon/ is in libkf5mailcommon-dev 4:16.04.2-2.
This file is owned by root:root, with mode 0o755.
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/usr/include/KF5/MailCommon/AccountConfigOrderDialog
/usr/include/KF5/MailCommon/AddTagDialog
/usr/include/KF5/MailCommon/BackupJob
/usr/include/KF5/MailCommon/CollectionAnnotationsAttribute
/usr/include/KF5/MailCommon/CollectionExpiryPage
/usr/include/KF5/MailCommon/CollectionGeneralPage
/usr/include/KF5/MailCommon/CollectionTypeUtil
/usr/include/KF5/MailCommon/DBusOperators
/usr/include/KF5/MailCommon/ExpireCollectionAttribute
/usr/include/KF5/MailCommon/FavoriteCollectionWidget
/usr/include/KF5/MailCommon/FilterAction
/usr/include/KF5/MailCommon/FilterActionDict
/usr/include/KF5/MailCommon/FilterImporterAbstract
/usr/include/KF5/MailCommon/FilterImporterBalsa
/usr/include/KF5/MailCommon/FilterImporterClawsMail
/usr/include/KF5/MailCommon/FilterImporterExporter
/usr/include/KF5/MailCommon/FilterLog
/usr/include/KF5/MailCommon/FilterManager
/usr/include/KF5/MailCommon/FolderCollection
/usr/include/KF5/MailCommon/FolderCollectionMonitor
/usr/include/KF5/MailCommon/FolderJob
/usr/include/KF5/MailCommon/FolderRequester
/usr/include/KF5/MailCommon/FolderSelectionDialog
/usr/include/KF5/MailCommon/FolderTreeView
/usr/include/KF5/MailCommon/FolderTreeWidget
/usr/include/KF5/MailCommon/FolderTreeWidgetProxyModel
/usr/include/KF5/MailCommon/IncidencesForWidget
/usr/include/KF5/MailCommon/ItemContext
/usr/include/KF5/MailCommon/JobScheduler
/usr/include/KF5/MailCommon/KMFilterDialog
/usr/include/KF5/MailCommon/MDNStateAttribute
/usr/include/KF5/MailCommon/MailFilter
/usr/include/KF5/MailCommon/MailInterfaces
/usr/include/KF5/MailCommon/MailKernel
/usr/include/KF5/MailCommon/MailUtil
/usr/include/KF5/MailCommon/MetaType
/usr/include/KF5/MailCommon/RedirectDialog
/usr/include/KF5/MailCommon/ResourceReadConfigFile
/usr/include/KF5/MailCommon/SearchPattern
/usr/include/KF5/MailCommon/SearchPatternEdit
/usr/include/KF5/MailCommon/SearchRule
/usr/include/KF5/MailCommon/SearchRuleStatus
/usr/include/KF5/MailCommon/SendMdnHandler
/usr/include/KF5/MailCommon/SnippetsManager
/usr/include/KF5/MailCommon/Tag
/usr/include/KF5/MailCommon/TagWidget