In human resources field there are many correspondences involved like offer letter, appointment letter, probation extension letter, confirmation letter, warning letter, termination letter, circular to employees, internal and external email communication etc etc. There are plenty of resource available on line.
You may refer them to gain knowledge and not for template purpose. Please try to understand the concept and then develop by your own.
show cause notice
increment letter and relieving letter
this link might be helpful in details and free samples to download of each letter: http://www.middleearthhr.com/hr_lett...d_formats.html