質問: 意味を教えてください i'll copy you in. はどういう意味ですか?
回答: copy sb in — phrasal verb with copy uk  /ˈkɒp.i/ us  /ˈkɑː.pi/ verb [ i or t ] to send someone a copy of an email that you are sending to someone else: i'll copy you in on all emails relating to the project. https://dictionary.cambridge.org/ja/dictionary/english/copy-sb-in