You can add a comma to an e-mail list in Microsoft Excel as long as your e-mail addresses are listed in separate, concurrent cells, such as a row or a column. You add commas by using a function called "CONCATENTATE." Once you add a comma to one e-mail address, you can use Excel's Auto Fill feature to copy the formula to the entire row or column.
Click in an empty cell, preferably next to or below the cell that contains the first e-mail address in the list.
Type "=CONCATENATE(Cell reference &", ")" with cell reference being the cell that contains the first e-mail address in the list. You should also press your "Spacebar" after typing the comma to ensure that your e-mail is separated by a comma and a space. For example, enter "=CONCATENATE(A2 & ",_")."
Press "Enter" on your keyboard to complete the function. The cell returns the value of "Sample@email.com, ".
Click in the concatenated cell to select it.
Place your mouse pointer over the small square in the lower-right corner of the cell. This square is called the "Fill Handle."
Click and drag across or down the cells you want to fill. Excel automatically copies and updates the function into all the selected cells.
If you place the CONCATENATE function in concurrent rows or columns, you can double-click the "Fill Handle." Excel will automatically fill the cells until it reaches a blank cell in the concurrent row or column.