Legal letter sent to wrong address

[OhWesternWind]

Hi - could anyone tell me what happens in this case? If a letter threatening court action is sent to a person's previous address, because the person taking action doesn't know their current address, and the person being taken to court only has a limited time to respond before the case goes to court, is this invalid because it's not gone to their current address?

Hope that makes sense! Thanks.

Service is by post to the last known address. Courts are often sympathetic to requests for more time.