Unless otherwise provided, a notice that the Retirement Agency must mail or file under this subtitle shall be: Made in writing; and Sent to the claimant at the claimant's address on file at the Retirement Agency by: First class mail, postage prepaid, or Personal delivery. Whenever a claimant is required to take some action or make an election within a required period after the date of the notice, 3 days shall be added to the required period, if delivery of the notice is made by first class mail.