People use "Dear Sir" to address a male person formally in written communication. There are a few synonyms that can be used instead of "Dear Sir" that convey the same level of formality and politeness. Some of these are "Dear Mr.," "Sir," "Gentleman," "Esteemed Sir," "Respected Sir," and "Honorable Sir." Each of these alternatives has a slightly different connotation, and some may be more suitable in certain situations than others. "Dear Mr." is an appropriate substitute if you know the recipient's name, while "Respected Sir" is a good option if you want to express your admiration or respect. Regardless of the synonym used, it is always important to ensure that the communication remains courteous, polite, and respectful.