The warrant typically only applies to things that normally contain personal correspondence, such as first class or priority mail. Anything else can be and is opened for inspection on a regular basis, especially if it's coming from someplace that may be suspect or is reasonably believed to be suspect, such as through direct observation.
The relevant codes are Section 24 § 241, Selection of packages (observation) and Section 24 § 242 Inspection of packages.
Don't send your pot through the post.
(post is archived)