邮件中有错字：

class ExampleMailer < ActionMailer::Base
  default from: "myemail@gmail.com"
  def sample_email(user)
    @user = user
    mail(to: @user.email, subject: 'sample email')
  end
end

在您的 production.rb ，您可以将用户名写为 myemail 。没关系。

And in your production.rb, you can write username as myemail. That's fine.

让我知道它是否无效。

Let me know if its not work..