Collection agencies often refuse to sign for recorded delivery items these days. Too many active shooters gunning for them and they don't want to be served. Its easier and just as good legally speaking - cheaper, too - to ask for a receipt for your 1st class item at the post office. A postmistress told me that. It workrd for me.
Rules of service in the CPR - a first class post to the last known address is accepted as proof of service even if you don't live there anymore so a receipt works fine.
Musashi.
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