excel-vba：将粗体字体指定给字符串文本中的行

I have a string element that contains several lines of text. If I use this string as an outlook body text though, they will have no format like bold font to specific lines. I would like to take this string and apply bold font to specific lines (e.g. to all which contain the symbol "@" with a for loop).I have a string element that contains several l