How to use option buttons on an Outlook custom form
Steps to use option buttons on a mail message
1.Open a new mail message.
2.On the Tools menu, point to Forms, and then click Design This Form.
3.Click the (P.2) tab of the form.
4.On the Form menu, click Control Toolbox.
5.Drag two OptionButton controls from the Control toolbox to the form page.
6.Right-click the first option button, and then click Properties on the shortcut menu.
7.On the Value tab of the Properties window, click New. Type My Color as the name of the field, and then click OK. Note that the field is a Text field. On the Value tab of the Properties window, the Property to use setting should be set to Value. Change the Value setting to Blue.
8.Click the Display tab of the Properties window, and then change the Caption to Blue. This is what will actually appear on the form. Click OK.
9.Right-click the second option button control on the form, and then click Properties on the shortcut menu.
10.On the Value tab of the Properties window, notice that the control is automatically bound to the same field that was created for the first option button. Change the Value to Red.
11.Click the Display tab of the Properties window, change the Caption to Red, and then click OK.
12.Publish the form to the Personal Form Library for testing purposes. To do this, on the Tools menu, point to Forms, and then click Publish Form. Set the Look in field to Personal Forms Library, type Optionbuttons as the name of the form, and then click Publish. When you are asked whether to enable the Save Form Definition with Item setting, click Yes.
13.Close and do not save changes to the form.
To use the form, follow these steps:
1.On the File menu, point to New, and then click Choose Form. Set the Look in field to Personal Forms Library, click the Optionbuttons form, and then click Open.
2.Address the form to yourself.
3.Click the P.2 tab of the form, click the Red option button, and then click Send.
4.Open the item in the Inbox, click the P.2 tab of the form, and you will see that Red is selected. If you enter form design mode and click the All Fields page of the form, you will see that the My Color field contains the value Red.
Source:
How to use option buttons on an Outlook custom form
Same steps applied if you want to add checkbox,textbox, etc. make sure they have their own value.