Hello, Murat!
Thank you for the example and sorry for replying that late.
InternetMailTexts contain various formats of message. Most time it is 1 or 2 items and if you look at TextType property of its elements, you might notice that when there are 2 of them, they are often one of HTML type and another PlainText. So they are options of message that some email clients add to make messages readable on both: plain text and HTML recipient applications.
I could find only one message with 3 parts. And it was a message that Gmail collapses: first HTML part looked like a button with 3 dots in Gmail and the second part was the real message. Think, you should display to user all parts, but ones that before the last can be displayed collapsed. And if there is choice, prefer HTML to Plain text elements.
Hope, this helps.