When I receive a long email/message I feel I also need to answer with a long reply, that it would be rude to answer with 2 lines to an initial 20/30 lines messa

When I receive a long email/message I feel I also need to answer with a long reply, that it would be rude to answer with 2 lines to an initial 20/30 lines message. Maybe most people feel that way and when they receive a 3 lines initial message they feel confortable answering with 3 lines and they do it right away.