An employment verification letter is a letter written to confirm one's employment.
If the letter is being sent as a hard copy, then it should be in the proper business format, otherwise, if the letter is being emailed, it should have an appropriate subject line and proper grammar.
This letter confirms that [Name of Employee] is an employee of [Company Name]. She has been employed with us since [Starting Date of Employment]. Her current role is [Job Title].
If you need any additional information about [Name of Employee], please do not hesitate to contact me at [E-mail]. Thank you for your time.