Can a flea collar be legally mailed?

The correct answer indicates that mailing a flea collar is prohibited. This restriction often stems from regulations placed on certain hazardous materials or toxic substances that may pose risks during shipping. Flea collars typically contain chemicals that can be harmful if not managed properly, leading to their classification as items that shouldn't be sent through standard postal services.

In contrast, the other options suggest various conditions under which mailing a flea collar might be permissible, such as being sealed, labeled appropriately, or limited to specific seasons. However, these suggestions do not align with the established regulations governing the transportation of potentially dangerous items, which generally prohibits their mailing to ensure public safety and compliance with postal laws.