Moving mailboxes creating STMP email addresses

I need your help moving a number of mailboxes that I have from one forest to another. I am looking to move several domains but I am aware of the fact that when moving mailboxes across forest, the STMP email addresses are created however the format of [email protected] is used in generation of the primary since domain. Local is the default address policy.
I would like to avoid this situation of changing to particular domain. Is this possible and if it is possible how can it be done?
