21 CFR §17.7

1. (a)Service of a complaint may be made by:
   1. (1)Certified or registered mail or similar mail delivery service with a return receipt record reflecting receipt; or
   2. (2)Delivery in person to:
      1. (i)An individual respondent; or
      2. (ii)An officer or managing or general agent in the case of a corporation or unincorporated business.
2. (b)Proof of service, stating the name and address of the person on whom the complaint was served, and the manner and date of service, may be made by:
   1. (1)Affidavit or declaration under penalty of perjury of the individual serving the complaint by personal delivery;
   2. (2)A United States Postal Service or similar mail delivery service return receipt record reflecting receipt; or
   3. (3)Written acknowledgment of receipt by the respondent or by the respondent's counsel or authorized representative or agent.