So we have
2010 Exchange User@abc.com
2013 Exchange User@abc.com
We are migrating mailboxes from 2010 to 2013 and its all working. However there is one problem we are encountering: Exchange 2013 is not or can not forward emails to 2010 Exchange because it does not see it..
(Also to note these users are on different forests AD abc.com and AD abc1.com)
So what would be best way to forward emails to 2010 exchange users that have not been migrated yet?