"내일 편지를 보내줄 거야!"
Translation:I will send you the letter tomorrow.
I wrote "tomorrow i will send a letter," which was marked as wrong. However, there is no "you" specified in the sentence - yes, it is implied, but not definitely there as the translation suggests.
As I understand it, 주 in 보내줄 means the sending is for someone else's benefit. ..to or for someone else. To just 'send' would be 보내다 compared to 보내주다.
couldn't this be the imperative form as well? like, telling someone to send a letter tomorrow?
Im not fluent, but since there is no subject and its informal, i believe so