Requesting an experience letter from a company you left years ago works best if you address HR directly, give your employee ID, and attach a copy of your relieving letter or last payslip as proof. Older records take longer to retrieve, so ask early and allow a few weeks.
An experience letter confirms what you did and for how long. A relieving letter confirms that you completed your notice period and were formally released. New employers in India and the Gulf frequently ask for both.
Practice varies by jurisdiction. Many employers issue one as a matter of policy, and some labour laws require a service certificate on request. If they refuse, offer letters, payslips and tax records are usually accepted as alternative proof.
HR or the people operations team, with your reporting manager copied. Managers rarely have the authority to issue letterhead documents themselves.