Since you are in Maryland, I assume this is a Maryland probate. This answer is accurate for Maryland. When a person intiiates probate they are required to provide a list of names and addresses of those who are "Interested Persons." This is the List of Interested Persons. This is a term defined in the Maryland Code as: (1) everyone listed in the Will if there is a Will, these are known as Legatees (2) everyone who is a legal heir if there were no Will (these people are listed even if there is a Will because they are the ones who are most likely to challenge the Will), (3) any Executor and (4) any Personal Representative. A notice is then published in the newspaper once a week for 3 weeks. The Register of Wills then takes a copy of the newspaper notice and mails it by certified mail to all the people listed on the List of Interested Persons. Where the identity and or whereabouts of an interested person is unknown, the PR is required to try to locate them and then provide an affidavit of reasonable attempts to locate. There is no obligation for anyone to notify anyone who does not fit into the category of "Interested Person"
What state is the probate in?
California - answer is "yes" to notification by mail - "no" to a certified mail requirement. Also notice to those who would inherit had there been no Will.
This does not create an attorney/client relationship. This does not constitue legal advice. It is limited to facts of the question. You should consult an attorney in the appropriate state involved before making any decisions based on this answer