Limit Exchange 2013 to only send to specific domains

Hello all,

I have an Exchange Server 2013 and I would like to limit the allowed external Domains for all Users to just one.

So I created a new send connector with only this domain. Sending to this domain now works fine.

BUT:

All emails send to the other domains will be stuck in the queue for the configured retry time (1day) and then produce an NDR

#550 4.4.7 QUEUE.Expired; message expired in unreachable destination queue. Reason: A matching connector cannot be found to route the external recipient ##

QUESTION:

How can I get the NDR instantly with out the delay of one day. But I would like to still have a high retry value for all other errors.

Thank you,

Alex