You already have the function to send the email and in this function there is the correct message field?!
what you need to do is say that email is an html.
mail.IsBodyHtml = true;
Then you need to pass the message to upload already configured with the html tags, getting this way:
<b>Meu nome é Fulano</b>
<br/><br/>
Enviei uma mensagem de teste...
When you send this by its function, the email provider will turn the message tags into style and you will get the desired end result.
If you are picking up the text that your user is typing in a textarea for ex, you can use this plugin: https://www.aspsnippets.com/Articles/Rich-Text-Editor-WYSIWYG-Editor-in-ASPNet-MVC-5.aspx it already has the styles and when you pass parameter to its function, the message goes with the tags already implemented.
https://stackoverflow.com/questions/8628683/how-to-send-html-formatted-email
– Reginaldo Rigo