There are many formulas to add a comma after the first word in a cell. In case you have a list arranged across a column, you can replicate the formula across the list using the Fill option.

However, most email services and applications allow you to import addresses formatted using a comma-separated values file you export from Excel. Create your list of addresses in Excel using a ...

Your Excel spreadsheets may contain contact information that you'd like to store in one of these applications. By configuring your spreadsheet, you can convert it into a comma-delimited contact ...