Sorry for the delay @fabriziom1974
I received the message, thank you.
Technically the syntax in the email is incorrect since all the cid: references for inline images should follow a cid:local-part@domain-part syntax. Your sample message uses cid:file:logo which violates the syntax specified in RFC 2392.
That said, our intention is not necessarily to be that strict and we are looking into providing a workaround for this in future versions.