salary increment request letter

Dear Friends
I am working as an Administration Assistant in reputed firm, I am working in this company more than five years, I request several time to my superior to increase my salary but he didn’t take any action in this regard so I given him an official request letter , even it is also didn’t give me a result, so now I would like to send an official email request for him to raise my salary and I want to mention in that if any action will not take even after my mail, I will be forced to resign and look another job, Also I didn’t request last year for raise my salary even company raised salary for many other staffs. I need to send my son in school but this salary is not enough to even live in abroad, also every day I am getting new responsibilities. So kindly please help me to write a mail in this regard

Shijith