Most notice disputes are not about whether something was sent but about whether it arrived, and the rules answer that question with presumptions rather than evidence. A properly addressed letter is treated as received; an address on file is treated as current; a refused delivery is treated as delivered. This subject covers the receiving end: keeping an address current, what deemed receipt means, and what to do about a notice nobody ever saw.
Where an address on file is wrong, the outcome depends on why. A stale address is generally the recipient's risk, a transcription error by the sender is generally theirs, and an address that was never connected to the recipient rarely supports valid service at all. Establishing which situation applies is the first step in any argument about it.
