You basically have two options, to change your CUC configuration from the default to use the original called number to choose the mailbox, which is what you're seeing right now, to last redirecting number, BUT that is a system wide change, meaning this will be the behavior for the whole system.
Your other option, would be to configure a VM pilot with the mask fixed to 456, and apply it to that DN, OR use routing rules in CUC.
FYI, this has been asked plenty of times before at CSC, a search would have provided the answer.
HTH
java
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