Sorry for the inconvenience you are facing.
I have searched the forum and other documents and came across this Link
which states that
"The email header content-type is set by the server sending the email and contains information like To, From, Date, Time, etc. Some of which are displayed at the top of each email when viewing it in an email client."
You may please go through this link and share your findings with us.
If you still have some queries in this regard, then I need more clarification from you as I am somewhat unclear about if you are using Aspose's Exchange client to send email or retrieve emails from the exchange server? Also, can you please tell us if this happens only with this receiver or any other receiver server as well? I would also request you to provide us information about the exchange server you are using. If its possible for you to provide us a test account on your server, it will help us better analyze your requirements and assist accordingly.