Is it allowed to mail a magnet?

The reason why it is permissible to mail a magnet only if it is under a certain strength relates to safety and regulatory guidelines established by postal services. Magnets can potentially interfere with electronic devices or other magnetic materials during transit, which is why there are restrictions based on their magnetic strength. By limiting the strength of the magnet that can be shipped, postal services ensure that the risk of interference and disruption is minimized. This approach helps to maintain safety standards for both the mail handlers and the items being shipped.

The other options suggest either unrestricted mailing or outright prohibition, which doesn't align with the actual regulations that allow for specific conditions under which magnets may be sent. Proper labeling is typically important, but the core guideline centers around the strength restriction.