you need to checkout to

chatwoot/.env

inside it there are smtp setting, i use resend, they works fine

below for your reference:
SMTP_DOMAIN=smtp.resend.com

# Set the value to "mailhog" if using docker-compose for development environments,

# Set the value as "localhost" or your SMTP address in other environments

# If SMTP_ADDRESS is empty, Chatwoot would try to use sendmail(postfix)

SMTP_ADDRESS=smtp.resend.com

SMTP_PORT=587

SMTP_USERNAME=resend

SMTP_PASSWORD=re_yourpwd