When relief under section 89 of the Income Tax Act is available?
Relief under section 89 is available to an individual if he has received 

Salary or family pension in arrears  or in advance [Rule 21A (2)]
Gratuity in excess of  exemption under section 10(10)(ii)/(iii) [Rule 21A(3)]
Compensation on termination of employment [Rule 21A(4)]
Commuted pension in excess of exemption under section 10(10A)(i) [ Rule 21A(5)]

In case of payment received other than above CBDT can allow relief under section 89​ after examining each individual  case.  [Rule 21A (6)]