How to retain the gridlines from excel when I copy and paste to yahoo mail?
You are not going to achieve this with simple copy and paste. As a first step you have to print to a PDF file. There are two ways of retaining grid lines. The first is from the menu File>Page Setup>Sheet and tick Gridlines. The second is to format the cell borders. Either way, the grid lines get into the PDF file and you can copy that into the email.