Networking
Explanation DMARC (Domain-based Message Authentication, Reporting and Conformance) in all details
Explanation SPF (Sender Policy Framework) in all details
Explanation DKIM (DomainKeys Identified Mail) in all details
What is email envelope and email header
Postfix - how log email headers like From, To and Subject
ProFTPd Server with virtual users and in SFTP mode
Working with Vsftpd as FTPS server with virtual users and SSL certificates in Debian or Ubuntu
Understanding Key Differences Between FTP, FTPS and SFTP
Active and Passive FTP Simplified - Understanding FTP Ports
How to test SMTP and IMAP servers using the telnet command-line - part I - SMTP
