Many family names begin with O' or Mac or Mc . You should address her as Dear Ms. Smythe O'Callaghan . Many Irish people have given names that can be spelled in either Gaelic or English. For example, Se n , Liam , and M ir n are spelled John , William , and Maureen in English. Family names can also have either anglicized or traditional spelling.
Irish people can legally use both forms of their names, and commonly do so.
A man who signs himself Patrick MacGowan on a contract with a U.S. company might sign his checks P draig Mac Gabhann . In the Gaelic form of names, Mac and are both followed by a space. ACA indicates an accountant. Anyone who uses the title Dr. in a business context is probably a researcher, except that a senior executive might have received an honorary degree. Esq. is used, but rarely, by men only, in its British sense, not in its American sense.