I caused some havoc on our DC i have maile issues!

I got our international company to send me a list of their Global Address book.

So i managed to import them using CSVDE into our AD server.

So now i have 2 OU's Contacts1 and Contacts2

The Contact1 is the old GAL and Contacts2 the new GAL
Ive left it for quite some time and every now and again people complain they cant send a person mail they get a message from exchange saying there is a duplicate.

GAL2 contains most of GAL1 and more.
So yesterday i deleted GAL1!

Beeeeeg Mistake!

When people reply to mails that used to be in the Global address list, it comes back saying the object does not exist. (Which is true cus i have deleted it)
If they click reply then remove the conatct and reselect it from the GAL it works fine.

So it seems like even if you recreate a deleted entry it still somehow refer's to an old entry until you reselect it from the GAL.

So I have a backup of this on a AD VM , but how do i put it back ?

Pure speculation: restoring the system state from the backup will undo any AD changes since the backup

The reason you get the NDR is because Microsoft Exchange stamps objects (Mailboxes/Mail Enabled Contacts etc) with something called an LegacyExchangeDN.
Do you self a favour and google LegacyExchangeDN - there is a verified workaround and it pretty much involved stamping the contacts with this attribute manually or in bulk using ADmodify (can be downloaded)

PM me if you want further info or a bit of a helping hand