Basic-Concepts
Web Servers
Uptime
Internet
Programming
Version Control
Configuration Management
Virtualization
Databases
Mail Servers
Domain Name Servers
Some useful links to explain the concepts of Exim
http://www.cyberciti.biz/faq/exim-remove-all-messages-from-the-mail-queue/
http://www.electrictoolbox.com/show-exim-mail-queue/
https://www.ndchost.com/wiki/mail/exim-management