Outlook Addin - How can I set “High Importance” on email sent using C# in VSTO -

i want know how set headers of email on click on checkboxes. have created required checkboxes in formregion.

example: have checkbox named highimportance, on click of want change email header. tried this, doesn't work:

private void checkbox2_checkedchanged(object sender, eventargs e) {     this.outlookitem.importance = 2; } 

cast item mailitem, set importance.

private void checkbox1_checkedchanged(object sender, eventargs e) {   outlook.mailitem mymailitem = (outlook.mailitem)this.outlookitem;   mymailitem.importance = outlook.olimportance.olimportancehigh }