Traveler does not support rendering of an eml file attachment in body of host mail if the same eml file is embedded in the body like below.
Content-Type: message/rfc822; name=test mail.eml
So Traveler considers this eml file just as an attachment but does not render it in the body. This is due to various limitations of mobile device in rendering mail body.
So there is an Enhancement Request to support rendering of eml file in body of mail in mobile devices by Traveler. This Enhancement Request is submitted for Traveler version V11.