I mailed my return using certified mail, but tracking says ready for pickup, not delivered. I can't schedule redelivery to the IRS address either. What do I do?

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I was told by USPS that certified mail requires a signature and if nobody is there to sign, it goes back to the post office for pickup and if not picked up in 15 days it gets returned back to me. If it does get sent back to me, should I still use certified mail again and just hope they sign for it this time?