StoredPathName is a TFileName property that indicates the local file where the contents of the message part is stored. StoredPathName may contain a fully qualified path when the file is stored in a directory other than the current directory. 

StoredPathName is updated in Create to indicate the file used in creating the file attachment for the message. 

StoredPathName is also used in OpenLoadStream, and provides the file name for the internal TFileStream used to access the contents of the message part during encoding for subsequent transmission. 

StoredPathName is used in Destroy when FileIsTempFile contains True, and indicates the temporary file name to be deleted. 

During receipt of a file attachment message part, StoredPathName contains a temporary file name. The tempory file is deleted when receipt of the message part is completed. The only representation of the message part is in memory, and must be stored to a permanent location using SaveToFile to avoid data loss when the TIdMessage instance containing the message parts is freed.

TIdAttachmentFile.Create 

TIdAttachmentFile.Destroy 

TIdAttachmentFile.OpenLoadStream 

TIdAttachmentFile.FileIsTempFile