Some situation is better avoid Sidekiq like reporting the exception mail, so it’s always the best practices to building a Postfix Satellite SMTP service instead.
Install Postfix
yum install -y postfix cyrus-sasl-plain # cyrus-sasl-plain is no need for Ubuntu
yum erase -y sendmail* # In case Sendmail is installed
Configure
Similar to gmail or SendGrid, every mail service vendor offer different combination of setting, below is only apply to AliYun