1) Mail servers use various protocols and agents to manage email delivery. User agents handle reading and sending email, transport agents forward mail between machines, and delivery agents deliver mail to user mailboxes. 2) The Simple Mail Transfer Protocol (SMTP) is commonly used to transfer email between servers. SMTP transfers mail in a "push" manner, while protocols like POP and IMAP use a "pull" method for users to retrieve mail. 3) Dovecot is an open source IMAP and POP3 email server that is fast, simple to set up, and uses few system resources. Its self-optimizing indexes and self-healing abilities make it a good choice for small and large installations.

1. Mail Server
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2. Mail Server
E-Mail Basics
Linux provides e-mail servers,
which communicate with enduser systems and with other email servers to manage your email needs.
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3. Mail Server
1] User agent
for reading and sending mail
2] Transport agent
for forwarding mail between
machines.
3] Delivery agent
for delivering mail to the user mail
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4. Mail Server
The user agent act as the user
front end.
It consists of the application
layer programs like mail.
It hands over mail to the
transport agent.
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5. Mail Server
The transport agent is also
responsible for accepting mail
at the receivers end.
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6. Mail Server
The delivery agent receives
mail from the transport agent
and deliver it to the actual
user’s address.
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7. Mail Server
SMTP(Simple Mail Transfer Protocol)
Several protocols exist to manage
e-mail.
The most common of these is the
(SMTP), which is designed as a
push mail protocol, meaning that
the sending system initiates the
transfer.
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8. Mail Server
SMTP(Simple Mail Transfer Protocol)
SMTP is used through most of a mail delivery
system.
The final stage, though, often employs a
pull mail protocol, such as the Post
Office Protocol (POP) or the Internet
Message Access Protocol (IMAP). With
these protocols, the receiving system
initiates the transfer.
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9. Mail Server
SMTP(Simple Mail Transfer Protocol)
SMTP was designed to enable a
message to be relayed through an
arbitrary number of computers.
For instance, an end user might
compose a message, which is sent to
the local SMTP server.
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10. Mail Server
POP (Post Office Protocol)
This system might use its own
internal routing table to redirect
the message to another local
system, from which the message
might be read, either directly or via
a POP or IMAP server.
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11. Mail Server
POP (Post Office Protocol)
The POP and IMAP protocols can
be used by the local e-mail clients
to retrieve their e-mail from a
remote server.
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12. Mail Server
POP (Post Office Protocol)
Currently, these are the two most
prevalent protocols for e-mail
retrieval.
These can be used to connect to
your local server, as well as Webbased mail servers such as Gmail.
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13. Dovecot
Mail Server
Dovecot is an open source IMAP
and POP3 email server for
Linux/UNIX-like systems, written
with security primarily in mind.
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14. Dovecot
Mail Server
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.
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15. Dovecot
Mail Server
Most prominent (noticeable) features
1)Dovecot is among the highest
performing IMAP servers while still
supporting the standard mbox and
Maildir formats.
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16. Dovecot
Mail Server
Most prominent (noticeable) features
2) Dovecot's indexes are selfoptimizing.
They contain exactly what the
user's client commonly needs,
no more and no less.
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17. Dovecot
Mail Server
Most prominent (noticeable) features
3) Dovecot is self-healing.
It tries to fix most of the problems it
notices by itself, such as broken
index files.
The problems are however logged
so the administrator can later try to
figure out what caused them.
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18. Mail Server
MIME(multipurpose internet mail extension)
Today the mail facility is wildly
used to deliver multimedia
attachments.
There attachments are separate
file containing binary characters
which use the 8 character of ASCII
code.
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19. Mail Server
MIME(multipurpose internet mail extension)
There is a separate protocol which
handles these attachments MIMEmultipurpose internet mail
extension.
MIME extends the definition of mail
to include binary files and multiple
data format in single message.
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20. Mail Server
MIME(multipurpose internet mail extension)
MIME encodes a message before
sending which is sub-sequently
decoded at the other side by
MIME.
MIME message can be easily
exchange between them.
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21. Mail Server
Running Sendmail
Standard part of most Linux
distributions
One of the most popular mail
server programs on the Internet
Use Sendmail as an alternative to
expensive mail server programs
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(Microsoft Exchange Server)

22. Mail Server
Running Sendmail
Standard part of most Linux
distributions
One of the most popular mail
server programs on the Internet
Use Sendmail as an alternative to
expensive mail server programs
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(Microsoft Exchange Server)

23. Mail Server
Installing Sendmail
Quickly find out whether Sendmail
is installed on your system by
entering the following command
from a shell prompt:
$ rpm –q sendmail
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24. Mail Server
Installing Sendmail
If Sendmail has been installed, the
package version is displayed. If not,
the message ‘package sendmail is
not installed’ is displayed.
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25. Mail Server
Installing Sendmail
Check that m4 is installed by
running command
$ rpm –q m4
Check that sendmail –c4 is installed
by running the command
$ rpm –q sendmail –c4
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26. Mail Server
Installing Sendmail
m4 and sendmail –c4 are required
if you want to make changes to
your Sendmail configuration.
They are should be there if
Sendmail is installed.
It never hurts to check.
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27. Mail Server
Installing Sendmail
If Sendmail isn’t installed, instal by
following steps:
1)Insert the RedHat Linux
distribution CD in your CD drive.
2)When prompted to run the
Autorun file, click YES.
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(The Package Manager window opens)

28. Mail Server
Installing Sendmail
3) Click Forward
4) Scroll down the list and select
Mail Server.
5) Click Forward.
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29. Mail Server
Installing Sendmail
6) When Package Manager
program displays the list of
packages it processes to install,
Click Forward.
7) When the Package Manager
program is done, Click FINISH.
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30. Mail Server
Installing Sendmail
To install Sendmail manually,
$ rpm –ivh
/mnt/cdrom/RedHat/RPMS/sentmail*
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31. Mail Server
Modifying sendmail.mc
• Sendmail - one of the most difficult
program to configure that you will
ever encounter.
• In fact, the basic configuration file,
sendmail.cf is over 1000 lines long.
• You don’t want to mess with this file if
you can possibly avoid it.
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32. Mail Server
Modifying sendmail.mc
• The sendmail.cf configuration file
is generated automatically from a
much shorter file called
senndmail.mc.
• This file contains special macros
that are processed by a program
called m4.
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33. Mail Server
Modifying sendmail.mc
• The m4 program reads the macros in
the sendmail.mc file and expands
them to create the actual sendmail.cf
file.
• Even so, the sendmail.mc file is a
new hundred lines long.
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34. Mail Server
Modifying sendmail.mc
You can find the sendmail.mc and
sendmail.cf files in the
/etc/mail directory.
Before you edit these files, you should
make backup copies of the current
files.
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35. Mail Server
Modifying sendmail.mc
you can regenerate the
sendmail.cf file by commands:
$ cd /etc/mail
$ m4 sendmail.mc > sendmail.cf
$ server sendmail restart
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36. Mail Server
Modifying sendmail.mc
First command changes the current
working directory to /etc/mail.
Second command compiles the
sendmil.mc command into the
sendmail.cf command.
Third command restarts the Sendmail
service so that the changes will take
effect.
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37. Mail Server
Modifying sendmail.mc
Two strange conventions used in the
sendmail.mc file:
i) Comments don’t begin with at hash mark
(#), they begin with the letter dnl.
ii) Quotation marks must begin with a
backquote (`) and end with an apostrophe
(‘). So a properly quoted string looks like
this: MASQUERADE_AS(`mydomain.com’)
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38. Mail Server
Modifying sendmail.mc
Two of the more common
configuration changes that you
may need to make sendmail.mc:
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39. Mail Server
Modifying sendmail.mc
1) The default configuration allows
connections only from localhost.
If you want Sendmail to work as a server
for other computers on your network, look
for the following line in the sendmail.mc file:
DAEMON_OPTIONS(
`Port-smtp.Addr=127.0.0.1,
Name=MTA’)dnl
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40. Mail Server
Modifying sendmail.mc
2) Masquerading/hidden/concealed
allows all the mail being sent from
your domain to appear as if it came
from the domain (for example,
wally@cleaver.net) rather than
from the individual host (i.e.
wally@wally.cleaver.net).
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41. Mail Server
Modifying sendmail.mc
To enable masquerading, add lines
similar to these:
MASQUERADE_AS(`cleaver.net’)dnl
FEATURE (masquerade_envelope)dnl
FEATURE
(masquerade_entire_domain)dnl
MASQUERADE_DOMAIN(`cleaver.net’)dnl
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42. Mail Server
Setting up aliases
An alias – also known as a virtual user
– is an incoming e-mail address that is
automatically routed to local users.
i.e. you may want to create a generic
account such as sales@mydomain.com
and have all mail sent to that account
delivered to a user named willie.
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43. Mail Server
Setting up aliases
To do that, you edit the file
/etc/mail/virtursers/
This file starts out empty.
To create a virtual users, just like
the incoming e-mail address
followed by the actual recipient.
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44. Mail Server
Setting up aliases
For example, here’s a virturusers file
that defines several aliases:
sales@mydomain.com
willie
bob@mydomain.com
robert
marketing@mydomain.com
robert
After you make changes, you should restart
the Sendmail service.
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45. Mail Server
SPAM - Sendmail
• Spam artists – unscrupulous / dishonest /
corrupt marketers who clutter the Internet
with millions of unsolicited emails – are
constantly on the prowl for unprotected
Sendmail servers, which they can use to
launch their spam campaigns.
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46. Mail Server
SPAM - Sendmail
• If you don’t protect your server, sooner or
later a spammer will coax your computer
into spending almost all its time sending out
the spammer’s e-mail.
• To protect your server from becoming an
indentured spam servant, you can configure
it to refuse any mail that merely wants to use
your computer to relay messages to other
computers.
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