Formal — diplomatic protocol, official reception, awards ceremonies. Don't use it for everyday politeness; that's 礼貌 (lǐmào). 礼遇 specifically means 'special honored treatment,' not just 'good manners.'
memory
礼 (ceremony, ritual) + 遇 (to encounter, treat) = 'ritual treatment' — i.e. the formal way you receive a respected guest.
