1 Pa. Code § 33.31
Orders, notices and other documents originating with an agency, including forms of agency action, complaints and similar process and other documents designated by the agency for this purpose, shall be served by the office of the agency by mail, except when service by another method shall be specifically required by the agency, by mailing a copy thereof to the person to be served, addressed to the person designated in the initial pleading or submittal at his principal office or place of business. If service is not accomplished by mail, it may be effected by anyone authorized by the agency in the manner provided in 231 Pa. Code Rules 400-441 (relating to service of original process).
1 Pa. Code § 33.31
This section cited in 4 Pa. Code §265.4 (relating to appeals-level III); 4 Pa. Code §607a.6 (relating to order to show cause); 7 Pa. Code §179.9 (relating to service by the Commission); 16 Pa. Code §42.34 (relating to motions); 25 Pa. Code § 1.5 (relating to procedures); 25 Pa. Code §1021.33 (relating to service by the Board); 34 Pa. Code §49.11 (relating to service of orders, notices and duty of owner to post address); 34 Pa. Code §60.10 (relating to service of orders and notices); 34 Pa. Code §111.13 (relating to processing of appeals and cross appeals); 34 Pa. Code §131.32 (relating to petitions except petitions for joinder and challenge proceedings); 40 Pa. Code §15.44 (relating to service); 40 Pa. Code § 17.4 (relating to legal representation); 40 Pa. Code §17.13 (relating to protests/intervention procedure); 52 Pa. Code §1.53 (relating to service by the Commission); 52 Pa. Code §1001.51 (relating to service by the Authority); 55 Pa. Code §41.23 (relating to proof of service); 55 Pa. Code §41.24 (relating to certificate of service); 58 Pa. Code §51.23 (relating to order to show cause); 58 Pa. Code §491a.5 (relating to service); 61 Pa. Code §703.5 (relating to other submissions); 61 Pa. Code §703.6 (relating to service); and 67 Pa. Code §491.8 (relating to service).