It's not necessary. Inquiry, also known as inquiry, refers to the process that one party to a transaction sends an oral or written inquiry about the terms of the transaction to the other party in order to buy or sell a certain commodity. There are all kinds of inquiry methods, some just send an inquiry letter, but you don't have to send an inquiry letter, because some are very refreshing, you can make an inquiry directly by phone, or through QQ, email and so on. Inquiry letter is a letter written by the buyer to the seller asking about the commodity transaction.