SMTP, Sender header, and non-ASCII characters

[Midiar]

In TIdMessage.GenerateHeader, the From header is set using EncodeAddress, so non-ASCII characters are displayed correctly. 
The Sender header, however, is set directly, so that non-ASCII characters in TIdMessage.Sender.Name are substituted by "?".

Is that by design? Because of a standard, or because of actual behaviour by servers?

::tor