'보내다' is similar to '부치다'. but '보내다' have broader meaning than '부치다'. 보내다 > 부치다 ( '부치다' can't apply to human being ) ex) '보내다' → 사람을『보내다』(send a messenger) BUT 사람을『부치다』(X) 아이를 학교에『보내다』(send[put] a boy to school) BUT 아이를 학교에『부치다』(X) 당신을 떠나『보내고』 싶지 않아요(I don't want to leave you.) BUT 당신을 떠나『부치고』 싶지 않아요(X) '부치다' → 편지를『부치다』(send a letter) AND 편지를『보내다』(O) 기차로 물건을『부치다』(ship goods by rail) AND 기차로 물건을『보내다』(O) ㅂirregular verb/adjective rule is: When a word stem with final consonant ㅂ + a particle start with vowel, ㅂ changed 우 or 오. * ㅂ => 오 (only with 아 vowel) => 와 돕다, 곱다. 돕(다) + 아요 => 도와요 곱(다) + 아요 => 고와요 돕(다) + 으면 => 도우면 곱(다) + 으면 => 고우면 * ㅂ => 우 어렵다, 쉽다, 덥다, 춥다, 귀엽다, 입다, 아름답다, 맵다, 눕다, 줍다. 덥(다) + 어요 => 더워요 는데 is not starting with vowel, so there is no change. 돕(다) + 는데 => 돕는데 Also refer to https://www.italki.com/question/256216

I know this is a late reply because I just saw this now. But I think it will be easier to understand "부치다" as "ship" [verb]. Like, 택배를 부쳤어요. (I shipped the package) meanwhile 보내다 is "send". I send my kid to school, 아이를 학교에 보내요. please correct me if I am wrong.