LoadTypesFromOS is a Boolean property that indicates if MIME types defined in the operating sysyem should be used when populating the MIME types used in TIdMIMETable. 

The default value for LoadTypesFromOS is True as assigned in the constructor for the object instance. 

LoadTypesFromOS is examined when building the cached MIME types in the BuildCache method and the OnBuildCache event handler handler has not been assigned. 

Use OnBuildCache to control populating MIME type entries in the table when thje default values from the operating system are not desired. 

Use LoadFromStrings to load the MIME type mapping table from a specified string list. 

Use AddMimeType to manually create aMIME type mapping for the table.

OnBuildCache 

BuildCache 

LoadFromStrings 

AddMimeType