My rental property in Burlington city NJ gets a very high volume of " to resident" and other junk mail addressed to previous tenants. In the past i had not had seperate mailboxes for each unit but my current tenants have requested to do so. Is there some trick to getting this done or do i just put up the 2 mailboxes and its up to the mail man to figure out what to do with general mail that is not assigned to a particular Unit?

The resident can request that all standard mail not be delivered.  That stops a lot of unwanted mail however also stops those needed bed bath and beyond discount postcards.  

And it won’t stop first class.