Information from user defined field into Excel

In outlook 2016 is a user defined field with the name "ID". In that field the user can fill in his identification for a specifik e-mail by cell editing.
With VBA:

.Range("D" & EmailRow).Value = Item.Subject ' Subject

the information of subject is written into Excel. How can I get the user defined field "ID" information in the same way?

Do I need to define a variable?
If the answer is "yes", how do I realise that?