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It's definitely not a very professional approach to offer without an interview/ meeting at any company. It may be a scam if it has other dubious angles like an unknown company/ unverified email sender or caller/ too lucrative offer / request to pay a small sum before getting the offer/ or anything that rings fake bells.
However, if the recruiting manager knows you personally or has worked with you before then he may send over the offer after a candid discussion on phone/ in person. I have seen this happen before, although it's not very common!