I Hope This Doesn't Find You by Ann Liang

Unforgettable, snarky, and romantic, I Hope This Doesn't Find You is Never Have I Ever meets To All the Boys I've Loved Before if Lara Jean wrote hate emails instead of love letters.
Sadie Wen is perfect on paper: school captain, valedictorian, and a "pleasure to have in class." It’s not easy, but she has a trick to keep her model-student smile plastered on her face at all times: she channels all her frustrations into her email drafts. She'd never send them of course -- she'd rather die than hurt anyone's feelings -- but it's a relief to let loose on her power-hungry English teacher or a freeloading classmate taking credit for Sadie's work.
All her most vehemently worded emails are directed at her infuriating cocaptain, Julius Gong, whose arrogance and competitive streak have irked Sadie since they were kids. "You're attention starved and self-obsessed and unbearably vain . . . I really hope your comb breaks and you run out of whatever expensive hair products you've been using to make your hair appear deceptively soft . . ."
Sadie doesn't have to hold back in her emails, because nobody will ever read them . . . that is, until they're accidentally sent out.
Overnight, Sadie’s carefully crafted, conflict-free life is turned upside down. It's her worst nightmare -- now everyone at school knows what she really thinks of them, and they're not afraid to tell her what they really think of her either. But amidst the chaos, there's one person growing to appreciate the "real" Sadie -- Julius, the only boy she's sworn to hate . . . .