Find and Stop the Spamming in Qmail

Mail forwading in sendmail can be done in 2 ways, locally and remotely.If you want to redirect a mail within the local domain you can make use of the /etc/aliases for remote domains set and entry on the virtusertable. 

Mail group and aliasing
ftp-group:root,user1,user2

the above is an entry in the /etc/aliases file ,where ftp-group is your mail group and root,user1,user2 are your setted aliases. Which means mail sended to ftp-group will be recieved by all the three.

Spamming involves sending unwanted electronic communication and is often considered junk e-mail. Spammers lure individuals to read e-mails through enticing words in the subject line. The majority of spam is related to commercial advertising promoting questionable products or services. Often, sending spam is an attempt to commit identity theft or other types of fraud over the Internet.

Types of Spamming

However, when averaged out over the course of the year, 50% of spam falls into the following categories:

Adult content
Health
IT
Personal finance
Education and training
When you get spammed by others though it consumes your mail space apart from that it creates a traffic and let your server down at times due to low bandwidth.

Prevention Methods

• Spam Assassin
• SPF record
• DNS Blacklist
• Disable open relay
• Anti-Spamware
  

• /etc/mail/access :The access database file is created to accept or reject mail from particular/selected domains.For eg., you may choose to reject all mail coming from known spammers, or to accept to relay all mail from your local network.since relaying is denied by default with the newer versions of sendmial.So this file is more like a anti-spam feature in sendmail.

localhost.localdomain RELAY
localhost RELAY
192.168.1. OK

spammer@aol.com                 REJECT
cyberspammer.com                REJECT
doctor.com           550        Doctor, whenever I eat Hormel products, 

I feel a strong urge to throw up violently.  What can I do about this?

     Note:By default we have OK which means it accept the particular domain. 

• /etc/mail/aliases: An alias allows sendmail to redirect mail sent to given address. This mail can be redirected to another email address,a file, or piped through a program.Alias can only be set in local network.Any changes in this file will get updated after running make in /etc/mail to update your database.

  Eg:
  admin:root---> all mail sended to admin will be redirected to root.
  team1:shiju,rahul,ashley--->team1 is the mailbox which contain a set of alias list.
  So team1@example.com will redirect the mail to rahul,ashley and shiju.

• /etc/mail/local-host-names:It has a list of domain and hostnames sendmail is to be receiving mail for.[all local-host-names and domains]
  Eg:shiju.com
  mail.shiju.com
  *.shiju.com
  
  
• /etc/mail/mailer.conf:It specifies which MTA is used in the mail server.
  Eg:
  Exim,Postix
  
  
• /etc/mail/mailertable:This file is used to route a domain to an different hosts or Simply for mail forwarding.For Example all mail coming from network 192.168. route to mail.shiju.com and all email for mydomain.com will be automatically forwarded to a mail server joe@mail.com
  Eg:
  192.168. smtp:mail.shiju.com
  mydomain.com smtp:joe@mail.com

• /etc/mail/sendmail.cf:Main configuration file for sendmail.Keep your Hands off unless you know what you are doing.Do all editing in sendmail.mc. Use “m4 sendmail.mc>sendmail.cf” command to update the changes.

• /etc/mail/virtusertable:The virtusertable maps mail addresses for virtual domains and mailboxes to real mailboxes. These mailboxes can be local, remote, aliases defined in /etc/mail/aliases or files.
  Eg:
  root@example.com root
  shiju@example.com joe@www.domain.net
  @example.com joe
  
  

What's the difference between POP and IMAP?

Changing interface IP address for exim mail server.

EXIM   

Install Exim from source

Then execute the following commands to create your mail log and mail storage storage (MSA)

#mkdir -p /var/spool/mail 
#mkdir -p /var/log/exim 
#chown exim:exim /var/spool/mail 
#chown exim:adm /var/log/exim 
#chmod 1777 /var/spool/mail
#chmod 2750 /var/log/exim

#ln -s /usr/sbin/exim /usr/lib/sendmail 
#ln -s /usr/sbin/exim /usr/sbin/sendmail 
 
Creating a secure runtime configuration

All the functionality of Exim is controlled from /etc/exim.conf

Edit the new /etc/exim.conf and find the following entries:
 



primary_hostname = mail.example.com (mail domain) or hostname(localhost)

never_users = exim


host_lookup = * (reverse DNS lookup on all incoming  IP calls, in order to get the true host name.)


# Set this the the name that appears after the @ in your email address 

local_domains =

# Set this to localhost and the name that appears after the @ 


# in your email address separated by a colon.


# for example localhost:enterprise-hr.com for Patrick.


host_accept_relay = 127.0.0.1: 


# Add in the range used by machines on your LAN.  If you #do not have a


# LAN or are unsure, don't edit this.  Example: #for a LAN with IP


# Address range 192.168.0.0/24, you put #that in here:  


# host_accept_relay = 127.0.0.1:192.168.0.0/24



Everything else in /etc/exim.conf should just work nicely.
 
Starting Exim
 

killall sendmail
/usr/sbin/exim -bd -q15m 
 
Note:Use telnet to check whether exim runs in 25 port
telnet localhost 25
 
Exim is now listening on port 25 for mail from the machine itself or
from the address range you specified in /etc/exim.conf

To Send Mail 

exim - v user1@localhost 
Heloooo
.

Note:If you have configured properly you will see a Log message showing mail transfer completed. 
Check 
# tail /var/log/exim/[exim_maillog,exim_rejectlog,exim_paniclog] for log details.
# cat /var/spool/mail/user1 [To read the mail]


Thank You.