Section 13(3)(a) in The Adjudicating Authority (Procedure) Regulations, 2013
(a)The service of summon or notice upon the defendant or respondent may ordinarily be made by,-(i)Dasti i.e. delivering or tendering personally; or(ii)registered post acknowledgement due (AD), or by speed post or courier service; or(iii)Electronic mail (e-mail) or by fax message.(iv)If any summon or notice, when tendered, is refused or if the person on whom the summon to be served refuses to sign an acknowledgment of service, then the complainant or applicant shall make a report to this effect and in such event, such summon or notice shall be deemed to have been served.