Concept of Send-Mail
When we are going to send any mail from one system to other user, then the SEND-MAIL server will work three states. These states are given below,
I. MUA - Mail User Agent
II. MTA - Mail Transfer Agent
III. MDA - Mail Delivery Agent
There are some important protocols, which are used for sending or receiving mail,
a. SMTP - Simple Mail Transfer Protocol is used for sending mail and the port number is 25.
b. IMAP - Internet Mail Access Protocol is used for receiving mail from other, and the port number is 143.
c. POP - Post Office Protocol is also used for receiving the mail and the port number is 110.
We need to install three rpm for SEND-MAIL server,
To install Sendmail
[root@www root]# rpm -q sendmail
sendmail-8.12.11-4.6
ð This package is need for server side to send mail or e-mail.
[root@www root]# rpm -q sendmail-cf
sendmail-cf-8.12.11-4.6
ð To configure send-mail server we need this package. After installation the rpm, it creates two configuration files named sendmail-cf and sendmail-mc in /etc/mail/ directory. The original configuration file’s name of send-mail is sendmail-cf but it is not editable by user. For this reason we need another package to configure the server.
[root@www root]# rpm -q m4
m4-1.4.1-15
ð m4 package is a compiler which converts sendmail-mc file to sendmail-cf. That means while we shall edit the sendmail-mc file to configure new configuration of sendmail we must use m4 command.
To configure sendmail
1). The configuration file of the SEND-MAIL server is "sendmail.cf"
[root@www root]# vi /etc/mail/sendmail.cf
ð But, don't edit this file. To change this file we have to go to other file called "sendmail.mc".
[root@www root]# vi /etc/mail/sendmail.mc
divert(-1)dnl
dnl #
dnl # This is the sendmail macro config file for m4. If you make changes to
dnl # /etc/mail/sendmail.mc, you will need to regenerate the
dnl # /etc/mail/sendmail.cf file by confirming that the sendmail-cf package is
dnl # installed and then performing a
dnl #
dnl # make -C /etc/mail
dnl #
include(`/usr/share/sendmail-cf/m4/cf.m4')dnl
VERSIONID(`setup for Red Hat Linux')dnl
OSTYPE(`linux')dnl
dnl #
dnl # default logging level is 9, you might want to set it higher to
dnl # debug the configuration
dnl #
dnl define(`confLOG_LEVEL', `9')dnl
dnl #
dnl # Uncomment and edit the following line if your outgoing mail needs to
dnl # be sent out through an external mail server:
dnl #
dnl define(`SMART_HOST',`smtp.your.provider')
dnl #
define(`confDEF_USER_ID',``
dnl define(`confAUTO_REBUILD')dnl
define(`confTO_CONNECT', `1m')dnl
define(`confTRY_NULL_MX_LIST',true)dnl
define(`confDONT_PROBE_INTERFACES',true)dnl
define(`PROCMAIL_MAILER_PATH',`/usr/bin/procmail')dnl
define(`ALIAS_FILE', `/etc/aliases')dnl
define(`STATUS_FILE', `/var/log/mail/statistics')dnl
define(`UUCP_MAILER_MAX', `2000000')dnl
define(`confUSERDB_SPEC', `/etc/mail/userdb.db')dnl
define(`confPRIVACY_FLAGS', `authwarnings,novrfy,noexpn,restrictqrun')dnl
define(`confAUTH_OPTIONS', `A')dnl
dnl #
dnl # The following allows relaying if the user authenticates, and disallows
dnl # plaintext authentication (PLAIN/LOGIN) on non-TLS links
dnl #
dnl define(`confAUTH_OPTIONS', `A p')dnl
dnl #
dnl # PLAIN is the preferred plaintext authentication method and used by
dnl # Mozilla Mail and Evolution, though Outlook Express and other MUAs do
dnl # use LOGIN. Other mechanisms should be used if the connection is not
dnl # guaranteed secure.
dnl # Please remember that saslauthd needs to be running for AUTH.
dnl #
dnl TRUST_AUTH_MECH(`EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
dnl define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
dnl #
dnl # Rudimentary information on creating certificates for sendmail TLS:
dnl # make -C /usr/share/ssl/certs usage
dnl # or use the included makecert.sh script
dnl #
define(`CERT_DIR',`/etc/mail/certs')
define(`confCACERT_PATH',`CERT_DIR')
define(`confCACERT',`CERT_DIR/cacert.pem')
define(`confSERVER_CERT',`CERT_DIR/cert.pem')
define(`confSERVER_KEY',`CERT_DIR/key.pem')
define(`confCLIENT_CERT',`CERT_DIR/cert.pem')
define(`confCLIENT_KEY',`CERT_DIR/key.pem')
dnl #
dnl # This allows sendmail to use a keyfile that is shared with OpenLDAP's
dnl # slapd, which requires the file to be readble by group ldap
dnl #
dnl define(`confDONT_BLAME_SENDMAIL',`groupreadablekeyfile')dnl
dnl #
dnl define(`confTO_QUEUEWARN', `4h')dnl
dnl define(`confTO_QUEUERETURN', `5d')dnl
dnl define(`confQUEUE_LA', `12')dnl
dnl define(`confREFUSE_LA', `18')dnl
define(`confTO_IDENT', `0')dnl
dnl FEATURE(delay_checks)dnl
FEATURE(`no_default_msa',`dnl')dnl
FEATURE(`smrsh',`/usr/sbin/smrsh')dnl
FEATURE(`mailertable',`hash -o /etc/mail/mailertable.db')dnl
FEATURE(`virtusertable',`hash -o /etc/mail/virtusertable.db')dnl
FEATURE(redirect)dnl
FEATURE(always_add_domain)dnl
FEATURE(use_cw_file)dnl
FEATURE(use_ct_file)dnl
dnl #
dnl # The -t option will retry delivery if e.g. the user runs over his quota.
dnl #
FEATURE(local_procmail,`',`procmail -t -Y -a $h -d $u')dnl
FEATURE(`access_db',`hash -T
FEATURE(`blacklist_recipients')dnl
EXPOSED_USER(`root')dnl
dnl #
dnl # The following causes sendmail to only listen on the IPv4 loopback address
dnl # 127.0.0.1 and not on any other network devices. Remove the loopback
dnl # address restriction to accept email from the internet or intranet.
dnl #
DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl
dnl #
dnl # The following causes sendmail to additionally listen to port 587 for
dnl # mail from MUAs that authenticate. Roaming users who can't reach their
dnl # preferred sendmail daemon due to port 25 being blocked or redirected find
dnl # this useful.
dnl #
dnl DAEMON_OPTIONS(`Port=submission, Name=MSA, M=Ea')dnl
dnl #
dnl # The following causes sendmail to additionally listen to port 465, but
dnl # starting immediately in TLS mode upon connecting. Port 25 or 587 followed
dnl # by STARTTLS is preferred, but roaming clients using Outlook Express can't
dnl # do STARTTLS on ports other than 25. Mozilla Mail can ONLY use STARTTLS
dnl # and doesn't support the deprecated smtps; Evolution <1.1.1>
dnl # when SSL is enabled-- STARTTLS support is available in version 1.1.1.
dnl #
dnl # For this to work your OpenSSL certificates must be configured.
dnl #
dnl DAEMON_OPTIONS(`Port=smtps, Name=TLSMTA, M=s')dnl
dnl #
dnl # The following causes sendmail to additionally listen on the IPv6 loopback
dnl # device. Remove the loopback address restriction listen to the network.
dnl #
dnl DAEMON_OPTIONS(`port=smtp,Addr=::1, Name=MTA-v6, Family=inet6')dnl
dnl #
dnl # enable both ipv6 and ipv4 in sendmail:
dnl #
dnl DAEMON_OPTIONS(`Name=MTA-v4, Family=inet, Name=MTA-v6, Family=inet6')
dnl #
dnl # We strongly recommend not accepting unresolvable domains if you want to
dnl # protect yourself from spam. However, the laptop and users on computers
dnl # that do not have 24x7 DNS do need this.
dnl #
FEATURE(`accept_unresolvable_domains')dnl
dnl #
dnl FEATURE(`relay_based_on_MX')dnl
dnl #
dnl # Also accept email sent to "localhost.localdomain" as local email.
dnl #
LOCAL_DOMAIN(`localhost.localdomain')dnl
dnl #
dnl # The following example makes mail from this host and any additional
dnl # specified domains appear to be sent from mydomain.com
dnl #
dnl MASQUERADE_AS(`mydomain.com')dnl
dnl #
dnl # masquerade not just the headers, but the envelope as well
dnl #
dnl FEATURE(masquerade_envelope)dnl
dnl #
dnl # masquerade not just @mydomainalias.com, but @*.mydomainalias.com as well
dnl #
dnl FEATURE(masquerade_entire_domain)dnl
dnl #
dnl MASQUERADE_DOMAIN(localhost)dnl
dnl MASQUERADE_DOMAIN(localhost.localdomain)dnl
dnl MASQUERADE_DOMAIN(mydomainalias.com)dnl
dnl MASQUERADE_DOMAIN(mydomain.lan)dnl
MAILER(smtp)dnl
MAILER(procmail)dnl
ð Some lines of the file is started by dnl, it means that lines are not being read by the sendmail. We get a line in this file which starts with the option as DAEMON_OPTION (Boldly given in above). Comment that line by adding "dnl" before the line. Example,
dnl # DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl
2). Now we shall compile the sendmail.mc file by using the below command.
[root@www root]# m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
ð m4 is nothing but a compiler. It will convert the "sendmail.mc" file to "sendmail.cf" file.
3).
[root@localhost root]# service sendmail start
ð To start the send-mail server.
[root@www root]# sendmail -d0 -v
Version 8.12.11
Compiled with: DNSMAP HESIOD HES_GETMAILHOST LDAPMAP LOG MAP_REGEX
MATCHGECOS MILTER MIME7TO8 MIME8TO7 NAMED_BIND NETINET NETINET6
NETUNIX NEWDB NIS PIPELINING SASLv2 SCANF STARTTLS TCPWRAPPERS
USERDB USE_LDAP_INIT
============ SYSTEM IDENTITY (after readcf) ================
(short domain name) $w = www
(canonical domain name) $j = www.home.com
(subdomain name) $m = home.com
(node name) $k = www.home.com
========================================================
Recipient names must be specified
ð It will show the host name, domain name, FQDN etc.
4). To receive the mail, we need another rpm called "imap.rpm"
[root@localhost RPMS]# rpm -ivh imap.rpm
ð The post office protocol( pop ) also includes the "imap.rpm". The configuration file of pop is "ipop3",
[root@localhost root]# vi /etc/xinetd.d/ipop3
ð In the file, we should change the option "Disable" equal "no". Such that
Disable = no
Now start the xinetd service,
[root@localhost root]# service xinetd start
The
All the mails are stored in the directory called "/var/spool/mail",
[root@localhost root]# cd /var/spool/mail
ð Show all the mails.
In the user's home directory there is a file "mbox". All the mail is stored in this file.
[root@localhost root]# vi mbox
To give an alias name to individual or a group
[root@localhost root]# vi /etc/aliases
ð Some important lines of the file are given below,
#mailbox aliases
linux : Root
#person who should get root's mail
#sumon is a normal user
root : sumon
#Basic system aliases - There must be present
mygroup : sumon,azgar,root
ð When we send a mail to mygroup then this mail automatically send to sumon, azgar, and root user. After editing the "aliases" file we must be give the command as,
[root@localhost root]# newaliases
ð Now the aliases file will active.
[root@localhost root]# mail root@mail.iiht.com
[root@localhost root]# mail mygroup@mail.iiht.com
[root@localhost root]# mail mail.iiht.com
ð Those are the example for sending mail to users.
Note: For send-mail server, you must create first a Name Server (NS).
