When you register a vehicle while being out of state, you should allow 6 weeks for your registration documents to arrive by mail, and allow 90 days for your title certificate to arrive.
Do I have to contact you or the motor vehicle agency in another state?
You must contact the motor vehicle agency in the other state to determine if their laws require that you register your vehicles there. The definition of "resident" is different in each state.
Is it also possible to do it by mail?