very strange... I don't understand why it applies to the first one only. I made it work by saving each mail item afterwards. Also, you should "Add" the userproperty[VBA]'declare a variable fro mailitems
Dim myItem As MailItem

'loop through all the items in the selection
For Each myItem In myOlSel
myItem.UserProperties.Add("My storage Number", olText) = "111"
myItem.Save 'save it!
Next[/VBA]