1. informal way(btw similar aged people who's really close) ======================================================= sorry if my korean is bad. 내 한국어 실력이 별로 안좋다면 미안해. or more like korean expression being modest. sorry about my poor korean. 내 한국어 실력이 별로라서 미안해. *take care. 잘 지내. *thank you very much. 너무 고마워. 2. formal(the person who receive this mail, is older or not really close or for business purpose) sorry if my korean is bad. 제 한국어 실력이 모자라다면 죄송합니다.or more like korean expression being modest. sorry about my poor korean. 제 한국어 실력이 모자라서 죄송합니다. *take care. 안녕히 잘 지내십시오 or 평안히 잘 지내시기 바랍니다(extremly formal=usually for business), 안녕히 잘 지내세요 or 안녕히 잘 지내시구요(very formal=usually for older people or people who are not really close to you and you want to be formal and showing them respect), 잘 지내요 or 잘 지내구요(sorta formal=the person a little be older than you but not too much close but you and she or he feel a bit comfy and feel like friends a bit or the friends who just get to know each other, even they are your aged group) *thank you very much. 진심으로 감사드립니다. Thank you sincerely or 대단히 감사드립니다 thank you so much (extremly formal=for very older people or for business purpose) 정말 감사합니다/대단히 감사합니다( very formal but not extremly. so you can use this term to older people in general even for business purpose in person but not for letter really. but I still recommend 1st expression for business purpose. cuz it sounds more like official and formal) 정말로 감사드려요/대단히 감사드려요(formal but a bit ladylike.) 정말로 고맙습니다/대단히 고맙습니다(still formal but a bit casual than 감사합니다. you can use this expression when you are older than the person you talk with.)정말 고마워요/너무 고마워요(more casual than -습니다 term and a bit ladylike. but guys still can use it to close friends) hope it can be helpful for you. :) if you need to ask further, don't hesitate and contact me right away. :) Corean Big SIs