finalreport1182014

VIETNAM NATIONAL UNIVERSITY OF HCMC
INTERNATIONAL UNIVERSITY
INTERNSHIP REPORT
BY
NGUYEN LE CHANH DUY
BUILDING MAIL SERVER ON LINUX
FOR ENTERPRISE
Submitted to: School of Computer Science and Engineering
International University, VNU-HCM

August 2014
INTERNSHIP REPORT
by
Nguyen Le Chanh Duy
Submitted to: School of Computer Science and Engineering
International University, VNU-HCM
August 2014
Organization/Company: ATHENA
Address: 92 Nguyen Dinh Chieu street, Da Kao ward, district 1, Ho Chi Minh city,
Vietnam.
Phone number: 090 78 79 477-094 323 00 99-(08)38244041
Duration of the Internship: 8 weeks (16-06-2014 – 16-08-2014)
Supervisors during the Internship:
o Name: Mr. Vo Do Thang.
o Title: Director of ATHENA.
o Address: 92 Nguyen Dinh Chieu, Da Kao ward, district 1, HoChiMinh city,
Vietnam
o Email: Thangvo@athena.edu.vn
ii

ACKNOWLEDGMENTS
After 8 weeks of internship at ATHENA, i have completed my project “Building mail
server on Linux for enterprise” with the support from friends and instructor.
I want to thank ATHENA for providing me good conditions to complete my internship
project, especially, I want to thank Mr. Vo Do Thang who has instructed and supported
me during all the time of internship at ATHENA.
Moreover, I have learned new knowledge at ATHENA such as Linux server, Centos,
network, VPS…they will be helpful for my job in the future.
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TABLE OF CONTENTS
I. DESCRIPTION OF COMPANY/ORGANIZATION......................................................5
II. SUMMARY OF THE INTERNSHIP.............................................................................7
III. PLANNING ..................................................................................................................9
IV. INTERNSHIP ACTIVITIES & ACHIEVEMENTS...................................................11
A. Email Protocols..........................................................................................11
B. Email Structure..........................................................................................14
C. Mail Server on Linux for enterprise...........................................................16
D. System Requirement..................................................................................17
E. Start building the mail server.....................................................................17
V. INTERNSHIP ASSESSMENT.....................................................................................34
REFERENCES..................................................................................................................35
iv

DESCRIPTION OF COMPANY/ORGANIZATION
ATHENA is a center of education and training of IT fields. It was established in 2004.
This is the center in which many experienced IT engineers work and study in order to
contribute to the development of IT fields in Vietnam.
The major fields of ATHENA:
o ATHENA center focus deeply on education and training of system and network
security, network management and maintenance following the standard quality
of Microsoft, Cisco, Oracle, Linux LPI, CEH…Moreover, ATHENA center also
has the private program of education and training for some government
organizations.
o After 10 years, many trainees of ATHENA center do the job in IT fields for some
government organizations and also for the big companies.
o Besides education and training programs, ATHENA center also cooperate and
exchange technology with some universities such as university of technology,
university of information technology, natural and university of science…
The instructors of ATHENA:
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o ATHENA instructors graduate from many big universities in Vietnam. They all
have to get international certificates such as MCSA, MCSE, CCNA, CCNP,
Security+, CEH, Microsoft Certified Trainer…in order to work at ATHENA.
o ATHENA instructors usually go abroad to be trained about the new technologies
and then they transmit those new technologies to the trainees.
vi

SUMMARY OF THE INTERNSHIP
After 3 years in HCMC International University, I have taken many courses of Network
Engineering so I decided to take internship at ATHENA. Because, ATHENA is a center
that specializes in network and system fields. At ATHENA, I take a project that requires
me to build a mail server on Linux for enterprise.
First, I have to get used to new Linux OS: Centos 6.5. Although, I approached another
Linux OS in coursers in university. I must learn how to control Centos with commands in
terminal.
Second, I must build on local host in order to get used to the configuration of mail
services. Two Linux virtual machines need to be installed (server and client) to test the
mail exchange.
Next, I must correct bugs by myself. I can look for documents, solutions…from internet
or from friends to solve the problems. If it still does not work, I must discuss with the
instructor to get the solutions or the instructions.
Finally, I must build a mail server on VPS. Here, I have to set up putty to access the VPS
in order to configure. My mission is to make the VPS become a Linux mail server that
can connect with yahoo mail and gmail. If it does not exchange mail with gmail or yahoo
vii

mail, I must fix bugs. My work is done if the VPS works correctly as the instructor
requires.
viii

PLANNING
Week 1:
o Seeing the instructor to get the project.
o Reading and understanding document.
o Asking question if necessary.
o Writing report.
Week 2:
o Reading and understanding Linux OS.
o Get used to Centos 6.5
o Writing report.
Week 3:
o Setting up VMware.
o Setting up Centos 6.5 on 2 virtual machines (server and client).
o Installing telnet, postfix and dovecot services on server.
o Writing report.
Week 4:
o Configuring network (Ethernet, hosts…).
o Configuring postfix and dovecot
o Testing telnet service.
o Writing report.
Week 5:
o Installing squirrelmail on server and thunderbird on client.
o Configuring squirrelmail and thunderbird.
o Sending mail between server and client via squirrelmail and thunderbird.
o Writing report.
Week 6:
o Having a VPS.
o Installing telnet, postfix and dovecot service on VPS.
o Installing squirrelmail on VPS and thunderbird on the laptop.
o Writing report.
Week 7:
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o Configuring postfix and dovecot.
o Configuring squirrelmail and thunderbird.
o Exchange mail with gmail and yahoo mail.
o Writing report.
Week 8:
o Fix errors.
o Exchange mail with gmail and yahoo mail again.
o Writing final report.
o Having a project presentation.
x

INTERNSHIP ACTIVITIES AND ACHIEVEMENTS
A/ Email Protocols:
Interactions between email servers and clients are governed by email protocols.
The three most common email protocols are POP, IMAP. Most email software
operates under one of these (and many products support more than one).
The Post Office Protocol (currently in version 3, hence POP3) allows email client
software to retrieve email from a remote server. The Internet Message Access
Protocol (now in version 4 or IMAP4) allows a local email client to access email
messages that reside on a remote server. The SMTP (Simple Mail Transfer
Protocol) protocol is used by the Mail Transfer Agent (MTA) to deliver your
email to the recipient's mail server
1. Post Office Protocol (POP):
POP is the older design, and hails from an era when intermittent connection via
modem (dial-up) was the norm. POP allows users to retrieve email when
connected, and then act on the retrieved messages without needing to stay "on-
line." This is an important benefit when connection charges are expensive.
The basic POP procedure is to retrieve all inbound messages for storage on the
client, delete them on server, and then disconnect. (The email server functions
like a mailbox at the Post Office -- a temporary holding area until mail gets to its
final destination, your computer.)
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Outbound mail is generated on the client, and held for transmission to the email
server until the next time the user's connection is active. After it's uploaded, the
server forwards the outgoing mail to other email servers, until it reaches its final
destination.
Most POP clients also provide an option to leave copies of email on the server. In
this case, messages are only removed from the server when greater than a certain
"age" or when they have been explicitly deleted on the client. It's the copies on
the client that are considered the "real" ones, however, with those left on the
server merely temporary backups.
2. Internet Access Message Protocol (IMAP):
IMAP is the newer protocol and oriented toward a "connected" mode of
operation. The standard IMAP procedure is to leave messages on the
server instead of retrieving copies, so email is only accessible when "on-
line."
IMAP is more suited to a world of always-on connections, particularly the
fast connections offered by broadband mechanisms. Having to be
connected to read your email is a trivial obstacle when the connection is
always available. (It's a little like leaving your messages at the Post
Office, and going there every time you want to read them. That might be
difficult in the physical world, but it's easy in the virtual one.)
xii

Because messages remain on the server, until explicitly deleted by the
user, they can be accessed by multiple client computers -- an important
advantage when you use more than one computer to check your email.
IMAP does not preclude keeping copies on the client, but, in an inversion
of the way POP works, it's the server's copies that are considered the "real"
ones. That offers an important security benefit -- you won't lose your
email if, for some reason, your client computer's storage media fails.
IMAP has other advantages over POP (detailed in the links provided
below). It is the standard we recommend if you can't use MAPI.
3. The Simple Mail Transfer Protocol (SMTP):
At the risk of overloading you with information, you should know that
strictly speaking it's only the incoming mail that is handled by a POP or
IMAP protocol. Outgoing mail for both POP and IMAP clients uses the
Simple Mail Transfer Protocol (SMTP).
When you set up a POP or IMAP email account on email client software,
you must specify the name of the (POP or IMAP) mail server computer for
incoming mail. You must also specify the name of the (SMTP) server
computer for outgoing mail. These names are typically in the same form
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as Web addresses (e.g., "imap.med.miami.edu"). Depending on the client,
there may also be specifications for email directories and searching.
B/ Email Structure:
o Mail User Agent (MUA): is a program that allows you to receive and
send e-mail messages; it's usually just called an e-mail program. To use an
MUA such as Eudora or Microsoft Outlook, you install the MUA program
on your computer and then use it to download and store e-mail messages
to your computer; it will also allow you to read or write messages offline.
Web-based MUAs, such as Hotmail and Yahoo, store messages on their
own mail servers and allow access to them through a Web page. An MUA
is sometimes called an e-mail agent or an e-mail client.
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o Mail Transport Agent (MTA): is an application that receives incoming
e-mail from local users (people within the same domain) and remote
senders and forwards outgoing e-mail for delivery. A computer dedicated
to running such applications is also called a mail server. Microsoft
Exchange, qmail, Exim and sendmail are among the more common mail
server programs.
o Mail Delivery Agent (MDA): is the software and other systems that are
responsible for sending and receiving mail between systems. That is the
ONLY things MTAs do: they send and receive messages between systems.
MTAs use the SMTP (Simple Mail Transfer Protocol) to send and receive
messages.
o Mail Submission Agent (MSA): is a computer program or software
agent that receives electronic mail messages from a mail user
agent (MUA) and cooperates with a mail transfer agent (MTA) for
delivery of the mail. It uses a variant of the Simple Mail Transfer
Protocol (SMTP), as specified in RFC 6409.
o Mail Access Agent/ Mail Retrieval Agent (MAA/MRA): is
a computer application that retrieves or fetches e-mail from a remote mail
server and works with a mail delivery agent to deliver mail to a local or
remote email mailbox. MRAs may be external applications by themselves
xv

or be built into a bigger application like an MUA. Significant examples of
standalone MRAs include fetchmail, getmail and retchmail.
C/ Mail Server (Postfix, Dovecot…) for Enterprise on Linux:
This is a Linux mail server for small and medium companies/enterprises with low
investment. However, it is stable and effective.
o Postfix is Wietse Venema's mail server that started life at IBM research as
an alternative to the widely-used Sendmail program. Postfix attempts to be
fast, easy to administer, and secure. The outside has a definite Sendmail-
ish flavor, but the inside is completely different.
o Dovecot is an open source IMAP and POP3 email server for Linux/UNIX-
like systems, written with security primarily in mind. Dovecot is an
excellent choice for both small and large installations. It's fast, simple to
set up, requires no special administration and it uses very little memory.
xvi
Thunderbird, Outlook,
Squirrelmail…
POSTFIX
Authenticate
DOVECOT
MailStore
MailBox
(File
Linux)
PROCMAIL
SpamAssanssin

o SquirrelMail is a standards-based webmail package written in PHP. It
includes built-in pure PHP support for the IMAP and SMTP protocols, and
all pages render in pure HTML 4.0 (with no JavaScript required) for
maximum compatibility across browsers. It has very few requirements and
is very easy to configure and install. SquirrelMail has all the functionality
you would want from an email client, including strong MIME support,
address books, and folder manipulation.
D/ System Requirement:
o The linux system requires normal hardware support, a linux server with medium
configuration can work stably and effectively. For example, a mail server with
configuration: CPU Pentium III 600MHZ, RAM 256MB, HDD 40GB can serve
from 300 to 400 users.
o Soft wares are required to install on a Linux mail server:
• Operating System: Centos 6.5 running with command line.
• SMTP Server: Postfix 2.3.3
• POP3/IMAP Server: 1.0.7
• Web Mail: SquirrelMail 1.4.8
• Web Server: Apache 2.2.3
Depending on the requirements, all the soft wares can be updated to the
newer version.
E/ Start building the mail server:
I/ Starting with local host:
1. Configure static IP address:
Server:
xvii

# vi /etc/sysconfig/network-scripts/ifcfg-eth0
BOOTPROTO=static
IPADDR=192.168.1.245
NETMASK=255.255.255.0
GATEWAY=192.168.1.254
Client:
# vi /etc/sysconfig/network-scripts/ifcfg-eth0
BOOTPROTO=static
IPADDR=192.168.1.240
NETMASK=255.255.255.0
GATEWAY=192.168.1.250
2. Configure hostname:
# vi /etc/hosts
127.0.0.1 mail.athena.lab
129.168.1.245 mail.athena.lab
# vi /etc/sysconfig/network
NETWORKING=yes
NETWORKING_IPV6=yes
HOSTNAME=mail.athena.lab
3. Configure DNS:
The DNS is a hierarchical distributed naming system for computers,
services, or any resource connected to the Internet or a private network. It
associates various information with domain names assigned to each of the
participating entities. Most prominently, it translates easily
memorized domain names to the numerical IP addresses needed for the
purpose of locating computer services and devices worldwide. The
Domain Name System is an essential component of the functionality of
the Internet.
Install packages with command:
xviii

# rpm –ivh <packages>:
bind-9.8.2-0.17.rc1.el6_4.6.i686.rpm
bind-libs-9.8.2-0.17.rc1.el6_4.6.i686.rpm
bind-utils-9.8.2-0.17.rc1.el6_4.6.i686.rpm
Create file: /etc/named.conf
acl mynet {
192.168.1.0/24
};
options {
allow-transfer {none;};
directory” /var/named”;
query-source port 53;
query-source-v6 port 53;
dump-file “var/named/data/cache_dump.db”;
statistics-file “var/named/data/named_stats.txt”;
mamstatistics-file
“var/named/data/named_mem_stats.txt”;
notify yes;
};
zone “.” IN {
type hint;
file “named.root”;
};
zone “athena.lab” IN {
type master;
file “athena.lab.db”;
allow-query {mynet;};
};
zone “1.168.192.in-addr.arpa” {
type master;
file “1.168.192.in-addr.arpa.db”;
};
Create file: /var/named/named.root by downloading via internet with the
command: # wget http://www.internic.net/zones/named.root
Create file: /var/named/athena.lab
$TTL 86400
@ IN S0A dns.athena.lab. root. {
46 ; serial
3H ; refresh
xix

15M ; retry
1W ; expire
1D ; ttl
}
IN NS dns.athena.lab.
dns IN A 192.168.1.245
mail IN A 192.168.1.245
Create file: /var/named/1.168.192.in-addr.arpa.db:
$TTL 86400
@ IN S0A dns.athena.lab. root. {
46 ; serial
10800 ; refresh
900 ; retry
604800 ; expire
86400 ; ttl
}
@ IN NS dns.athena.lab.
1 IN PTR mail.athena.lab.
Restart named daemon:
# service named restart
Shut down firewall:
# service iptables stop
4. Install and configure Postfix service:
Install Postfix service with command:
# yum install postfix
Configure Postfix:
# vi /etc/postfix/main.cf
## Line 75 – Uncomment
myhostname = mail.athena.lab
mydomain = athena.lab
## Line 99 - Uncomment
xx

myorigin = $mydomain
## Line 116
inet_interfaces = all
## Line 164 –Add $mycomain
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
mynetworks_style = subnet
## Line 264 – Uncomment, Add networks
mynetworks = 192.168.1.0/24, 127.0.0.0/8
home_mailbox = Maildir/
Restart postfix:
# service postfix restart
# chkconfig postfix on
# netstat –nat | grep 25
Install Telnet service:
# yum install telnet telnet-server –y
Create users:
# useradd user1
# passwd user1
# useradd user2
# passwd user2
Telnet to server:
# telnet mail.athena.lab 25
Trying ::1…
Connected to mail.athena.lab.
Escape character is ‘^]’.
220 mail.athena.lab ESMTP Postfix
Send mail from user1 to user2:
mail from: user1@athena.lab
250 2.1.0 OK
rcpt to: user2@athena.lab
250 2.1.5 OK
xxi

data
354 End data with <CR><LF>.<CR><LF>
Testing
.
250 2.0.0 OK: queued as 1247AF434A
quit
221 2.0.0 Bye
Connection closed by foreign host.
5. Install and configure Dovecot service:
Install Dovecot service with command:
# yum install dovecot
Configure dovecot:
# vi /etc/dovecot/dovecot.conf
protocols = imap pop3 lmtp
## Line 26 – Uncomment, remove “,::”
listen = *
# vi /etc/dovecot/conf.d/10-auth.conf
disable_plaintext_auth = no
## Dòng 97 – Uncomment
auth_mechanisms = plain login
# vi /etc/dovecot/conf.d/10-mail.conf
mail_location = maildir:~/Maildir
# vi /etc/dovecot/conf.d/10-master.conf
port = 143
port = 993
port = 110
xxii

port = 995
mode = 0600
## Line 83 – Uncomment, sửa lại thành:
user = postfix
## Line 84 – Uncomment, sửa lại thành:
group = postfix
Restart dovecot and postfix service:
# service dovecot restart
6. Install and configure Mozilla Thunderbird:
Install thunderbird with command:
# yum install thunderbird
Create email account with thunderbird:
o Step 1: Access Mozilla Thunderbird
xxiii

o Step 2: Create a new account > Email
o Step 3: Yourname: user1 > Email address: user1@athena.lab > Password:
1234 > Remember password
o Step 4: Continue > Manual config
o Step 5: Incoming: 192.168.1.245 (IP server) > Outgoing: 192.168.1.245
o Step 6: Re-test > confirm security > done
Create email account for user2 as we do for user1
Restart postfix, dovecot service, then exchange mail between user1 and
user2 by using Mozilla Thunderbird.
7. Install and configure Squirrelmail:
Install squirrelmail with commands:
# rpm –Uvh http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-
8.noarch.rpm
# yum install squirrelmail
Configure squirrelmail:
# vi /etc/share/sbin/squirrelmail/config/conf.pl
o Step 1: Server Settings > Domain: athena.lab
o Step 2: Sendmail or SMTP > SMTP
o Step 3: R > D > dovecot
o Step 4: S to save > Q to quit
Restart postfix, dovecot and httpd service.
Exchange mail between user1 and user2 by accessing
http://<ipaddress>/webmail or http://<domain-name>/webmail
II/ Building mail server on VPS:
1. Install Putty to access the VPS
2. Register domain name:
xxiv

o Step 1: Access www.dot.tk to get a free domain name: athenacd.tk
o Step 2: Use DNS > Dot TK DNS Service
o Step 3: Host name: www.athenacd.tk > IP address: 14.0.31.168
Host name: athenacd.tk > IP address: 14.0.31.168
o Step 4: maintain this domain name in 3 months
o Step 5: Choose google account to manage this domain name
o Step 5: Sign in my.dot.tk > Go to domain > Modify
o Step 6: Add 2 records > Save changes
A Record > mail.athenacd.tk > 14.0.31.168
MX Record > athenacd.tk > mail.athenacd.tk
3. Configure DNS:
Install packages with command: rpm –ivh <packages>:
bind-9.8.2-0.17.rc1.el6_4.6.i686.rpm
bind-libs-9.8.2-0.17.rc1.el6_4.6.i686.rpm
bind-utils-9.8.2-0.17.rc1.el6_4.6.i686.rpm
Create file: /etc/named.conf
acl mynet {
14.0.31.160/27
};
options {
allow-transfer {none;};
directory” /var/named”;
query-source port 53;
xxvi

query-source-v6 port 53;
dump-file “var/named/data/cache_dump.db”;
statistics-file “var/named/data/named_stats.txt”;
mamstatistics-file
“var/named/data/named_mem_stats.txt”;
notify yes;
};
zone “.” IN {
type hint;
file “named.root”;
};
zone “athenacd.tk” IN{
type master;
file “athenacd.tk.db”;
};
zone “31.0.14.in-addr.arpa” {
type master;
file “31.0.14.in-addr.arpa.db”;
};
Create file: /var/named/named.root by downloading via internet with the
command: # wget http://www.internic.net/zones/named.root
Create file: /var/named/athena.tk
$TTL 86400
@ IN S0A dns.athenacd.tk. root. {
46 ; serial
3H ; refresh
15M ; retry
1W ; expire
1D ; ttl
}
IN NS dns.athenacd.tk.
IN MX 10 mail.athenacd.tk.
dns IN A 192.168.1.245
mail IN A 192.168.1.245
www IN CNAME athenacd.tk.
ftp IN CNAME athenacd.tk.
Create file: /var/named/31.0.14.in-addr.arpa.db:
xxvii

$TTL 86400
@ IN S0A dns.athenacd.tk. root. {
46 ; serial
10800 ; refresh
900 ; retry
604800 ; expire
86400 ; ttl
}
IN NS dns.athenacd.tk.
1 IN PTR dns.athenacd.tk.
2 IN PTR mail.athenacd.tk.
2. Install and configure Postfix service:
Install Postfix service with command:
# yum install postfix
Configure Postfix:
# vi /etc/postfix/main.cf
myhostname = mail.athenacd.tk
mydomain = athenacd.tk
myorigin = $mydomain
## Line 116
inet_interfaces = all
## Line 164 –Add $mycomain
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
mynetworks_style = subnet
## Line 264 – Uncomment, Add networks
mynetworks = 14.0.31.160/27, 127.0.0.0/8
home_mailbox = Maildir/
xxviii

Restart postfix:
# chkconfig postfix on
# netstat –nat | grep 25
Install Telnet service:
# yum install telnet telnet-server –y
Create users:
# useradd duy
# passwd duy
# useradd tien
# passwd tien
Telnet to server:
# telnet mail.athena.lab 25
Trying ::1…
Connected to mail.athena.lab.
Escape character is ‘^]’.
220 mail.athena.lab ESMTP Postfix
Send mail from duy to tien:
mail from: duy@athenacd.tk
250 2.1.0 OK
rcpt to: tien@athenacd.tk
250 2.1.5 OK
data
354 End data with <CR><LF>.<CR><LF>
Testing
.
250 2.0.0 OK: queued as 1247AF434A
quit
221 2.0.0 Bye
Connection closed by foreign host.
Shut down sendmail service and change from MTA to Postfix:
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# /etc/rc.d/init.d/sendmail stop
# chkconfig sendmail off
# alternatives –config mta
3. Install and configure Dovecot service:
Install Dovecot service with command:
# yum install dovecot
Configure dovecot:
# vi /etc/dovecot.conf
protocols = imap pop3 lmtp
## Line 26 – Uncomment, remove “,::”
listen = *
## Line 211 – Uncomment and add:
mail_location = maildir:~/Maildir
Restart dovecot and postfix service:
4. Install and configure Squirrelmail:
Install squirrelmail with commands:
xxx

# rpm –Uvh http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-
8.noarch.rpm
# yum install squirrelmail
Configure squirrelmail:
# vi /etc/share/sbin/squirrelmail/config/conf.pl
o Step 1: Server Settings > Domain: athena.lab
o Step 2: Sendmail or SMTP > SMTP
o Step 3: R > D > dovecot
o Step 4: S to save > Q to quit
# vi /etc/httpd/conf/httpd.conf
<VirtualHost*:80>
ServerName mail.athenacd.tk
DocumentRoot /usr/share/squirrelmail
</VirtualHost>
xxxi

Restart postfix, dovecot and httpd service:
# service named restart
# service httpd restart
Exchange mail between user1 and user2 by accessing
Exchange mail between users and yahoo mail, google mail by accessing
xxxii

INTERNSHIP ASSESSMENT
During the internship period, I have gained new knowledge and many experiences from
my project. Firstly, I must take time to research about the Centos in order to understand
how it works. After researching, I recognized the differences between Centos and the
other OS, moreover, I have learned the way to control the Centos by using commands in
terminal. Secondly, I had chance to work with a real server, thanks to that, I knew how to
make it run correctly and fix bugs when problems happen. Next, by learning, I have
understood deeply about the mail protocols, dns, network configuration, network
problems… All of the experiences and knowledge that I have gained from the internship
will be helpful for my future career, because now I am taking the courses of Network
Engineering in university and in the future, as an network engineer, I will face with many
problems of systems, network, servers… However, during the internship period, I found
myself lack of basic knowledge, so beside researching via internet, I also re-learned
myself some courses that I have taken before.
xxxiv

REFERENCES
athena.edu.vn/
it.med.miami.edu/x1111.xml
searchnetworking.techtarget.com/definition/mail-user-agent
searchsoa.techtarget.com/definition/mail-server
en.wikipedia.org/wiki/Mail_delivery_agent
en.wikipedia.org/wiki/Mail_submission_agent
en.wikipedia.org/wiki/Mail_retrieval_agent
en.wikipedia.org/wiki/Domain_Name_System
www.postfix.org/
www.dovecot.org/
squirrelmail.org/about/
xxxv

finalreport1182014

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finalreport1182014