I have two trunks in a separate ring group I want to forward to an extension's voice mailbox when not answered. The trunk ring group and extension ring group is programmed and working but I can't figure how to forward to mailbox on RNA. There are two extensions in the ring group. Either mailbox is OK. This group is separate from the rest of the users so I need it to operate the same way day or night modes

Easiest way. DIL those trunks to one of the extensions. Create a VE of THAT extension on the other extension and have it ring. Trunks will follow forwarding on first extension.

If possible, don't put one extension as VE on another one.

We have a customer, they have more then 15 VE on different extensions, they also put more REAL extensions as VEs on phones everywhere. It's really hard to figure out the call flow.

I am just wondering why cannot NEC change something.

They do, it's called trunk mapping on the intramail but probably beyond what he wants to do. The 9100 also have new features to ring multiple extensions (outside lines) as per version 4.0. VE's are easy to use setting the ringing is a bit much. But if you set them up the way I do on buttons they aren't using and in the same plans on all the phones it becomes very easy to manipulate.