There are two main ways to set up data validation for email addresses in Excel:

Method 1: Using a Custom Formula

1. Select the cells: Choose the cell(s) where you want to restrict data entry to valid email addresses.
2. Data Validation: Go to the "Data" tab and click "Data Validation" in the "Data Tools" group.
3. Allow: Custom: In the "Settings" tab of the Data Validation window, under "Allow," choose "Custom" from the dropdown menu.
4. Formula for Validation: In the "Formula" box, enter the following formula:

```excel
=AND(ISNUMBER(SEARCH("@",A1)), ISNUMBER(SEARCH(".",A1)), NOT(ISNUMBER(SEARCH(" ",A1))))
```

Explanation of the Formula:

- `ISNUMBER(SEARCH("@",A1))`: Checks if "@" symbol exists in the cell (A1 in this example, replace with your cell reference).
- `ISNUMBER(SEARCH(".",A1))`: Checks if a period (".") exists in the cell.
- `NOT(ISNUMBER(SEARCH(" ",A1)))`: Ensures there are no spaces in the email address.

Replace A1 with your actual cell reference if it's different.

5. Error Alert (Optional): In the "Input Message" and "Error Alert" tabs, you can customize messages to be displayed when users enter invalid data or hover over the cell.
6. Click OK: Click "OK" to close the Data Validation window and apply the rule.

Method 2: Using a List of Valid Emails (Less Flexible)

1. Select the cells: Choose the cell(s) where you want to restrict data entry.
2. Data Validation: Go to the "Data" tab and click "Data Validation" in the "Data Tools" group.
3. Allow: List: In the "Settings" tab of the Data Validation window, under "Allow," choose "List" from the dropdown menu.
4. Source: In the "Source" box, type your valid email addresses separated by commas (e.g., "[email address removed], [email address removed]").
5. Error Alert (Optional): Similar to method 1, you can customize message displays.
6. Click OK: Click "OK" to close the Data Validation window and apply the list restriction.

Choosing the Right Method:

- Custom Formula: This method is more flexible as it validates based on email address structure and is not limited to a predefined list.
- List of Valid Emails: This method is simpler to set up but only allows users to choose from the email addresses you provide.