As a real estate agent myself, it is important that my mailings arrive to my clients or prospective clients. A few times a year, I will send out flyers, holiday greeting cards and update on active/pending/sold listings in the neighborhood.
The title company which assists me sending out the mailers has a address validation system which they use to verify if the address is correct and can be delivered by USPS. It is less work for me and saves me money with bulk mailing when I let the title company does it. All I do is design the postcards or flyer, print them out, fold them and then send them to my title company and they will do the rest.