Add or paragraph in Textarea Text

Add or paragraph in Textarea Text

I am using textbox for allowing user to enter any text they want, then I
am emailing this text. I want to add paragraphs or
in textarea text for eg if user enters this
this is test this is test this is test this is test this is test this is test
this is test this is test this is test this is test this is test
Then the email wil appear with whole text in one line, I want it to appear
like two or three paragraphs something like this
<p> this is test this is test this is test </p>
<p> this is test this is test this is test </p>
How I can do this in C#