1. Mail Server Basic

2. Receiving Mail Process
When someone sends you an it moves from their client to their mail server. Their mail server then uses the recipient address to determine where the mail is supposed to go and delivers the to your mail server.
Your mail server stores the received in a mailbox until your mail client asks for it. This is where IMAP and POP enter the picture.

3. IMAP (Internet Message Access Protocol) and POP (Post Office Protocol)
IMAP and POP are the two most prevailing methods or protocols for retrieving from a mail server. Both of these protocols are supported by almost all popular mail client programs like Outlook, Thunderbird and Apple Mail.
When your mail client reads an it can either download the from the mail server to your local desktop and delete it from the mail server, or just allow you to see the contents, without saving it locally, similar to your viewing a webpage. In the first case, where you download an to your local machine, POP is used. In the second case, where you view the , it actually stays on the mail server.

4. Main differences POP – Downloads email locally
IMAP – Mail is stored on the mail server

5. Sending s SMTP
POP or IMAP, when you send an you will use some form of SMTP (Simple Mail Transfer Protocol), which totally different from IMAP and POP.   When you click on send on an message the mail client contacts the SMTP server that is part of your mail service. The server authenticates you using your login id and password and receives the message from your client. The mail server then looks up the recipient’s mail server and passes the message to that server. Your mail client then places the sent in either your local sent mail folder or in the case of IMAP the sent folder on the server.

6. SMTP Relay
SMTP Relay, which stands for Simple Mail Transfer Protocol, lets you send messages through your account using your existing service. For example, you can continue to use Microsoft Outlook to compose, receive, and send messages, but the actual messages are processed through our SMTP relaying services. This lets you bypass ISP restrictions on your outbound messages and allows you to use your professional looking address rather than a general address.

7. Spam control
Spam is often sent by mass mailing operations that use computers to send millions of messages in a short period of time. Spam has become a popular marketing tactic because it is cheap and easy to send. Also, many spammers set up their accounts overseas in countries where the government may be indifferent to their activities. Or they may use a free service to set up temporary accounts they can suspend or abandon once they have been reported. For these reasons, reporting spammers often involves a lot of effort with very limited impact.

8. Never respond to spam. This includes clicking on any of the advertisements included in the body of a spam . Once you respond to spam, the spammer knows your address is active. They then know they can send more spam to that address. Not only that, it also means they may add your address to databases they can use to spoof the “from” address in future spam s, a common practice among spammers that makes them hard to track and shut down.

9. Be careful when using the “unsubscribe” instructions at the bottom of s. Only use this option if you are receiving s you requested. If you didn’t request the s (such as by subscribing to a newsletter) chances are it’s just a trick to get you to click on the link and let the spammers know they have found an active address.

10. Do not share your primary password on bulletin boards or online forums
Do not share your primary password on bulletin boards or online forums. Just as with web pages, spammers can use software to scan these online communities for addresses they can add to their databases. Avoid using your primary address in online forms. It is recommended that you use a secondary address when you sign up for online services or make purchases online. Setting up a secondary address can be done through a free provider such as Microsoft’s Hotmail, Yahoo, or Google’s GMail.

11. Installation of Mailserver
Yum install postfix
Yum install dovecot
Modify mail server configuration
Service postfix start
Service dovecot start
Vi /etc/postfix/main.cf

12. Chapter 9 Router Configuration (Ospf, Rip) Webmin, usermin Team viewer
Telnet
SSH
SCP, rsync

13. Webmin
Webmin is a web-based interface for system administration for Unix. Using any modern web browser, you can setup user accounts, Apache, DNS, file sharing and much more. Webmin removes the need to manually edit Unix configuration files like /etc/passwd, and lets you manage a system from the console or remotely.
Download webmin.rpm file from google
Install webmin rpm file

14. Webmin
In a web browser, enter the https address of the server with the port number to access Webmin - for example:
-or-
You will need to enter the root password of the server running Webmin to use the Webmin interface and administer the server.

15. Team viewer
TeamViewer is a proprietary computer software package for remote control, desktop sharing, online meetings, web conferencing and file transfer between computers. The software operates with the Microsoft Windows, OS X, Linux, iOS, Android, Windows RT and Windows Phone operating systems. It is possible to access a machine running TeamViewer with a web browser. While the main focus of the application is remote control of computers, collaboration and presentation features are included.

16. What is Telnet?
Telnet is a user command and an underlying TCP/IP protocol for accessing remote computers. Through Telnet, an administrator or another user can access someone else's computer remotely. On the Web, HTTP and FTP protocols allow you to request specific files from remote computers, but not to actually be logged on as a user of that computer. With Telnet, you log on as a regular user with whatever privileges you may have been granted to the specific application and data on that computer.

17. SSH
Secure Shell (SSH) is a cryptographic network protocol for secure data communication, remote command-line login, remote command execution, and other secure network services between two networked computers that connects, via a secure channel over an insecure network, a server and a client (running SSH server and SSH client programs, respectively). The protocol specification distinguishes between two major versions that are referred to as SSH-1 and SSH-2.

18. SCP
Secure copy or SCP is a means of securely transferring computer files between a local host and a remote host or between two remote hosts. It is based on the Secure Shell (SSH) protocol.
scp SourceFile
scp TargetFilescp -r TargetFolder

19. rsync
rsync is a utility software and network protocol for Unix-like systems (with ports to Windows) that synchronizes files and directories from one location to another while minimizing data transfer by using delta encoding when appropriate
One of the earliest applications of rsync was to implement mirroring or backup for multiple Unix clients to a central Unix server using rsync/ssh and standard Unix accounts.

20. The example below is for automatical settings
The example below is for automatical settings. Ecxample ⇒ Copy files and directories in /var/www/html on a HostA[ ] to in /home/backup on HostB[ ].

21. Rsync - Synchronizes files and directories
~]# yum -y install rsync xinetd
~]# vi /etc/xinetd.d/rsync
# default: off # description: The rsync server is a good addition to an ftp server, as it \ #      allows crc checksumming etc. service rsync { disable
= no
# change
flags
= IPv6
socket_type
= stream
wait
= no
user
= root
server
= /usr/bin/rsync
server_args
= --daemon
log_on_failure
+= USERID }

22. [root@dlp ~]# /etc/rc.d/init.d/xinetd start 
Starting xinetd:[ OK ]
~]# chkconfig xinetd on
~]# mkdir /home/backup 
~]# vi /etc/rsyncd.conf
# any name you like
[website] # destination directory
path = /home/backup # Hosts you allow to copy (specify source Host)
hosts allow = hosts deny = * list = true uid = root gid = root read only = false

23. [2]Configure on Source Host.[root@www ~]# yum -y install rsync
~]# vi /etc/rsync_exclude.lst
# specify files or directories you'd like to exclude to copy
test test.txt

24. [3]It's OK. Execute rsync on Source Host like follows.
~]# rsync -avz --delete --exclude-from=/etc/rsync_exclude.lst /var/www/html/ ::website
# Add in cron if you'd like to run reguraly
~]# crontab -e
# run at 2:00 AM in a day * * * rsync -avz --delete --exclude-from=/etc/rsync_exclude.lst /var/www/html/ ::website

25. Packet Analysis by using TCPDUMP and WIRESHARK
TCPDUMP Command
Wireshark installation