If create the body property as
System.Net.Mail.MailMessage message = new System.Net.Mail.MailMessage(); message.Body =\"First Line \\n second line\";
In case you dont need the message body in html, turn it off:
message.IsBodyHtml = false;
then use e.g:
message.Body = "First line" + Environment.NewLine + "Second line";
but if you need to have it in html for some reason, use the html-tag:
message.Body = "First line Second line";