I am not a frequent user of HSA and the related issues and read IRS Pub 969 reg HSA but could not find clear answers of the following points:

• Does contribution to HSA require “Earned Income”?
• Is there any income level after which HSA contribution is disallowed?
• Is there any income level after which HSA contribution is allowed but “not deductible”?
• An active employee of a major corporation normally has full medical and dental insurance coverage from the employer after paying a nominal share of medical and dental insurance premium.  Such an employee does not need to have a separate HDHP “COVERAGE” and covered by no other coverage EXCEPT “Other Health Coverage”.  Can such an employee still contribute to HAS and claim a tax deduction?
• I know of many major companies referred to above contribute to HSA of its employee/s and show the amount in W-2 Box 12 with W code.  If the employer can contribute to such an employee, why not the employee can make addl contr to max out?
• Is there any $ limit (assuming limited to $4,150 for Single and $8,300 for Family coverage) for an employer to contribute to HSA of an employee before it becomes taxable?
• Tax Free Distribution ONLY for expenses not reimbursed by HDHP? Does it mean the TP needs to have an EoB showing the rejection of the med ins claim?
• Can a TP e.g. 35 Yrs who is unemployed and uninsured contribute to HSA?