Is it legal to mail my sample?
For cannabis, no. For hemp, yes. On March 4, 2019, The United States Postal Service (USPS) released an advisory titled “Acceptance Criteria for Cannabidiol (CBD) Oil and Products Containing CBD”. Then, on June 6, 2019, The USPS issued an updated policy contained inside Postal Bulletin 22521 (pages 4-5) regarding mailing hemp and hemp-derived CBD products.
In this bulletin, The USPS says that to be in compliance, hemp and hemp products may be mailed if the hemp was grown according to the requirements of the 2014 Farm Bill, including that the Total THC concentration is ≤0.3 percent:
Under Postal Service regulations, including Publication 52, part 212, mailers are responsible for their own compliance with all laws and regulations governing mailability. Following this revision, mailers will also be responsible for retaining documentation which shows that they are complying with all such laws. A mailer is not required to present the documentation at the time of mailing, but such documentation may be requested either at that time or on a later date if there is doubt about the item’s mailability or the addressee’s ability to legally receive it. This process is consistent with existing regulations governing questions about mailability of restricted matter. See Publication 52 § 413.