_MailItem.SendUsingAccount Property
Office 2010
Namespace:
Microsoft.Office.Interop.Outlook
Assembly: Microsoft.Office.Interop.Outlook (in Microsoft.Office.Interop.Outlook.dll)
The SendUsingAccount property can be used to specify the account that should be used to send the MailItem when the Send method is called. This property returns Nothing (null in C#) if the account specified for the MailItem no longer exists.