Why is SparkPost not sending messages?

Question

Ruby on Rails

Hello everyone) I uploaded the rails application on Heroku. In the rail application, authentication using e-mail. For this case, I connected SparkPost. I wrote in production.rb:
config.action_mailer.smtp_settings = {
address: ENV.fetch("SPARKPOST_SMTP_HOST"),
port: 587,
domain: "bart2005.herokuapp.com",
authentication: "plain",
enable_starttls_auto: true,
user_name: ENV.fetch("SPARKPOST_SMTP_USERNAME"),
password: ENV.fetch("SPARKPOST_SMTP_PASSWORD")
}
Heroku sends messages, but they don't arrive in the mail. SparkPost also shows that the message has been sent. But there is nothing in the mail. I don't know how to solve the problem. I hope for your help) Thank you)