Generally speaking serving someone by hand - or personally as it is known by statute - is the best method of service.  Other methods are permitted and can be used but they are easily contested.  Service by mail is generally done as a two part service method: serving someone else over 18 at your home or affixing the summons to your home and then mailing.  So mailing alone is not generally done.  Ask his attorney about an affidavit admitting service as well.  Better yet, get an attorney for your interests. You should really not rely on his attorney's advice here or in any matter throughout your divorce. His interests are adverse to yours. Good luck.