tnef | TNEF is a program for unpacking MIME attachments of type | Email library

I'm using MailKit v2.8 to parse data out of emails in using IMAP to connect to a Microsoft Exchange 2013 account. The body of messages being sent to my Exchange inbox will be "text/plain" 100% of the time. This process works completely fine for new emails (and has been in production use for a couple months), however replies/forwards to those emails are being converted to HTML presumably by Exchange when fetching. The header of the reply email on the server still specifies that the message body is "text/plain." Outlook also displays the response in plain text, but for some reason when I try to fetch the TextPart of the message summary using MailKit, it is returning null.

MailKit email fetching code:

I am working with C# Outlook Object Model (with a little bit of C++ extended MAPI for decoding TNEF for RTF mails) and am trying to find a way to get the attachments from a mail I have used the tnef decode on (I opened this mail as a shareditem to access its contents), and add these attachments into a new mailitem. What I am observing with these attachments is that they either contain a filename with "UTF8 Hex: xxxx.msg" for message attachments, or shows null for attachment.filename, and the display name shows "UTF8 Hex: xxxx". I know these attachments without filename are pdf/docx files since I attached them myself for testing, but there's no way to identify that from the hex encoded displayname and null filename. (Where xxxx represents a long string of hexadecimals)

My usual go to when attaching HTML attachments when I am doing this is to use the attachment.FileName and do a attachment.SaveAsFile(filename), then doing a newmailitem.Attachments.Add(savedfile) but with the filename not found in the attachment and the displayname not showing anything helpful, I am lost on how I should do the same for RTF mails.

Any help would be much appreciated!