Internet Direct (Indy) Version 9.0.2 Beta
TIdEntityHeaderInfo.LastModified
Indicates the date and time a server resource was modified.

property LastModified: TDateTime;
Description
LastModified is a TDateTime property that indicates the date and time when the origin server believes the most recent version of a resource was modified. An origin server must not send a LastModified date which is later than the server time of message origination in Date. An origin server should send LastModified whenever possible.