I worked in a company, one of the biggest internet portal in my country. I was a team member whose responsibility was keeping mail infrastructure always up and available. More than 1 million page and several thousand mail client. All systems related with us were opensource, having CentOS as OS, qmail as mail server and php as programming language. Besides, I used AWS for hosting my domain, docker for preparing my working environment and some open source softwares for my daily needs like git and ansible.