PostItem.BeforeCheckNames Event (Outlook)
Occurs just before Microsoft Outlook starts resolving names in the recipient collection for an item (which is an instance of the parent object).
You use the BeforeCheckNames event in VBScript, but the event does not fire when an e-mail name is resolved on the form.
The event does not fire under the following circumstances:
You customized a Journal Entry form and then resolved a contact in the Contacts field.
You customized a Contact form and then resolved a contact in the Contacts field.
You customized any type of form and Outlook automatically resolved the name in the background.
You programmatically created and resolved a recipient.