What is the legal requirement for a defendant if they do not acknowledge service by mail?

The legal requirement for a defendant who does not acknowledge service by mail is that they must pay costs for personal service. When a defendant does not acknowledge service, this typically means that a formal process of serving the defendant is required to ensure that they are properly notified about the lawsuit. In many jurisdictions, if personal service is necessary because the defendant did not acknowledge the original service by mail, the plaintiff may then seek to serve the defendant personally, which incurs additional costs. Thus, the defendant may be held responsible for these costs since their failure to acknowledge service by mail necessitated a more formal and potentially costly method of service.

It is also worth noting that the other options do not accurately reflect the procedural requirements. Automatic dismissal does not occur; rather, the case may proceed with the plaintiff taking necessary steps to ensure proper service. The notion of a "second chance" to acknowledge service is not typically provided in this context, as the service must still be effectual. Moreover, while a defendant might contest the adequacy of service through a motion, this is not the primary legal requirement when service by mail is not acknowledged. Instead, the obligation to pay for personal service is a clear response to the failure to acknowledge the original service method.