Make your resume and resume differ from those of other candidates. As such, you should never start your resume with such general salutations as dear sir, or dear sir. Normally, when a company posts publicly a recruitment ad, it will surely address the name, address and contact number so as the resumes may be sent to correct address.
The employers are very busy as they may receive hundreds of resumes and resumes each day from different candidates. So, think carefully before you send your resume and resume to an employer is a good way to win over other candidates.