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==MAIL SERVER RESOURCESOVERVIEW & PREPARATION== {{Admon/important|Warning|Your lab 3 must be complete with a functioning DNS server for your domain before this lab will work.}}

* [https://prezi.com/iuk-advzak_o/mail-servers-postfix/ OPS335 Mail Server Notes ] Course Note providing Concepts and Overview Believe it or not, this is a simple diagram of mail server setup* [httpyou sending an email to someone else://www.fredshack.com/docs/postfix.html Postfix for Dummies] Good Basic Guide to setup Postfix MTA

==OVERVIEW & PREPARATION==This lab will show you how to set up a Mail User Agent ('''PostfixMUA''' email server (), using the '''MTAmailx''') package on your '''VM2vm2''' machine to send and receive e-mails on your local VM. In this case, the '''VM3Postfix''' machines. You will also be setting up on package which represents your '''VM2MTA''' is most likely already installed and running on your local VM. In addition to sending and receiving emails on your Local VM, you will also be able to send a text-based e-mail from your '''VM3vm2 machine''' machines the to your '''mailxSeneca mail account''' package ('''MUA''') to allow users to send and receive text-based mail messages. You should will also be able learn how to send email make multiple MTAs in the same network collaborate in sending emails. In addition, you will learn where the message store (MS) is located that stores mail messages until they are viewed and either deleted or transferred to your Seneca College email accountother folders.

The diagram below shows Although, you will not be able to receive mail messages from outside sources (such as your Seneca email account), this lab acts as a starting point in order to run a basic email server. You are NOT required to go into tremendous depth (just the layout minimum requirements). For example, we will not go over every aspect of the Postfix MTA service, but you should know what it represents and what this lab should be able is its main purpose, as opposed to accomplishthe following:[https://en.wikipedia.org/wiki/Postfix_%28software%29#Architecture complex diagram 1] , [https://www.credativ.de/blog/postfix-architecture-overview complex diagram 2].

* [http://www.simplehelp.net/2008/12/01/how-to-send-email-from-the-linux-command-line/ Mail Send Command] (examples how to send e-mail using mail command)* [Imagehttp://www.johnkerl.org/doc/mail-how-to.html#prompt_commands View and Manage Received e-mail Mesages] (Common commands to view and manage received email-setupmessages)* [https://support.google.pngcom/mail/answer/29436?hl=en Reading Full Email Headers](Explanation of message header information)* [http://wiki.dovecot.org/MailServerOverview Here's an overview](common mail server terms)

==INVESTIGATION 1: INSTALL & SETUP THE MAIL TRANSFER AGENT We will be using a simple text-based '''Mail User Agent (MTAMUA)==''' called '''mailx''' in this lab to '''both send and receive''' mail messages within your '''vm2''' machine and to '''only send''' mail messages from your '''vm2''' machine to your Seneca e-mail account.

{{Admon/important|Prerequistites|<ol><li>Ensure <u>all</u> machines have been updated and that the '''clocks NOTE:''' Because you're using private IP addresses and no external DNS servers are set pointing to the correct date and timeyour network, you '''.<bru>cannot</liu><li>Due ''' send e-mail messages from outside your environment to the changes made in this lab3, your '''you will now need your vm1 running (as the DNS server)vm2''' in order for any of your virtual machines to be able to use the internetmachine.</li></ol>}}

=== Confirm Network Connections Installing the Mail User Agent (MUA)===

Before proceeding with this lab, we need to confirm our machines have connectivity to '''Perform the Internet before we can install and start sending e-mail messages.following Steps:'''

#Make certain you are in your '''Perform vm2''' machine.#Install the following steps'''mailx''' application (MUA) using yum:'''NOTE:''' You can refer to the link below to acquaint yourself on how to send e-mail messages using '''mailx''' application:<br> [http://www.simplehelp.net/2008/12/01/how-to-send-email-from-the-linux-command-line/ Mail Send Command Examples]

#Make certain that you can connect to the Internet on ===Sending a Mail Message from your Host vm2 Machine via web-browser. Since your host should be using '''VM1''' as its '''DNS server''', you will need to make certain that the '''VM1''' machine is running as well.#Start a web-browser on your '''Host Machine''', and access your Seneca e-mail account (https://myseneca.ca).#Confirm that you can access the web from your '''VM2''' machine. You can install the '''wget''' or ly'''n'''x applications in order to test this for your text-based server.<br>'''NOTE:''' you should not have to authenticate yourself on the guest machine.Email Account===

===Install {{Admon/important|Note|These instructions no longer work reliably. You can still send email to your own email server, and Configure Postfix Package (MTA) on look at the server logs to see that it did really get sent. But it probably won't be accepted for one of a VM===multitude of good reasons. If it doesn't work for you: don't worry about it for lab submission purposes.}}

We will now be installing the postfix application which will act as the Mail Transfer Agent ('''test to see if your MTA''') that will send and receive for your vm2 machine is correctly running by sending email messages from your vm2 machine to your Seneca e-mail messages between various server.<br>In our case, between our servers '''vm2''' and '''vm3''', as well as between our '''vm2''' server and an outside server: '''Seneca College''' (https://myseneca.ca)account.

#Switch to Make certain you are still in your '''VM2vm2''' machine.#Check the status of the Test email from your machine by sending an email to your '''sendmailSeneca email account''' service by using the '''systemctl''' command. If the sendmail service is running, use the ''systemctl'' command to stop and disable that service. #Issue the following command to install the '''Postfix''' application (MTA):<br>'''yum install postfix'''<br><br>#What is the purpose of installing the postfix application in terms of using email -mail? Record your answer in your lab logbook.#We need to <u>configure</u> the postfix application (i.e. our MTA) to recognize our recentlys "Lab4a -created domain name that we setup in lab3.test1" <brYour Seneca email address>Edit the Postfix configuration file: '''/etc/postfix/main.cf''' and edit this file to contain only the contents displayed below:<br><br>'''mydomain = senecaID.orgNOTE:'''<br>after you type in the body of the mail message, move to an empty line, and then press the key combination '''myorigin = $mydomain&lt;ctrl&gt;&lt;d&gt;'''<br>'''mynetworks = 127.0.0to send the message.0/8, 192.168.X.0/24'''<br>'''relay_domains ='''<br>'''inet_interfaces=all'''#Check your Seneca email account (Inbox / Junk Email Folder) to see if you got the email (note that it may take a <bru>few minutes to arrive<br/u>Your MTA has the ability to resolve "fake" public address , so you may also wish to try an actual user alternate email account name. For example, if you have a user account called "msaul"one like gmail, etc). When you can have the MTA resolve the fake name "murray.saul" to the account name "msaul". In order to do this you need to create an alias which is contained in receive that email, make a note of the MTA's alias filereturn address.<br><br>#Edit If you did not receive the '''/etc/postfix/aliases''' file and add mail, check the mail logs on your first name as an alias vm2 machine to be resolved to your VM2's account name:<br><br>'''your-first-name''' &nbsp; &nbsp; &nbsp; '''your-vm2-regular-username'''<br><br>determine any errors messages that would indicate a mail server setup problem.#In order Once you have succeeded in sending the first email, send a second email to update the MTA's database for the newly-create alias, issue same destination using the following command:<br>'''postalias hash:/etc/aliases'''mail -r "someone@hacker.com (Canadian Revenue Agency)" -s "Lab4a - test2" <br><brYour Seneca email address>#Finally, Check your email to start and enable your MTAsee if you got the email. If you did, issue make a note of the following commands:'''systemctl start postfixreturn address.service'''<br>'''systemctl enable postfix.service'''<br><br>#Check How would you think that including the '''/var/log/messages-r''' file option could be used by penetration hackers to gain access to a computer system? What sort of steps do you think should be taken to see that your MTA server started without error If there are any errors, correct them before continuing.help prevent this type of attack from happening?

==INVESTIGATION 2We will be using the '''Postfix''' application as the '''MTA''', and we will be setting it up on your '''vm2''' and '''vm3''' machines. They will act as the "sending" email servers for your internal network. You will be able to send email out of your network, and receive email from within your network, but you will '''<u>not</u>''' receive email from outside of your network due to the following reasons: INSTALL &amp; SETUP THE MAIL USER AGENT * Individuals outside of your domain will never find the MX records because there are no other DNS servers pointing to your DNS server (MUAi.e. you haven't paid for it)==.* Even if the individuals could read your MX records, your local network is using IP addresses on a '''private subnet''', which is not routeable on the Internet, so it cannot be reached from outside of your system.

=== Installing '''Perform the Mail User Agent (MUA)===following steps:'''

#The '''Perform postfix''' application should be installed by default. If it isn't, install it.#Postfix is capable of sending email with the default configuration, so start and enable this service, and verify that the postfix service is running.#Look for the running postfix service in the list of listening ports by issuing the following Stepscommand:'''<br><source>ss -atnp</source>#Which service is postfix running? Locate the port used by SMTP, and look for connections with the state LISTEN (i.e. currently listening).#Write your observations in your lab logbook.

#Make certain you are in your '''vm2''' machine.#Issue === Testing the following command connection to install the '''mailx''' application (MUA):<br>'''yum install mailx'''<br><br>#Refer to the link below to acquaint yourself on how to use the '''mailx''' application:<br> [http://www.binarytides.com/linux-mail-command-examples/ mail command examples and additional utilities]Postfix Service ===

===Testing mail with We will be demonstrating the internet===use of the '''nc''' application to test that the postfix service is running and listening.

# If the '''nc''Perform ' command is not installed on your vm2 machine, install it (install '''nc''' command for your '''vm3''' as well).# Connect from your '''vm2''' to itself using the '''nc''' command by issuing the following stepscommand:<br><source >nc localhost 25</source># You should see a response: <br><source >220 vm2.yourdomain.ops ESMTP Postfix</source># You could theoretically use SMTP commands to send an email here, but this would be a very unusual use of your mail server. You have an '''MUA''' for a reason.#Enter the command '''QUIT''' to close the connection to the server, then '''<ctrl>-c''' to terminate the nc command.

#Make certain you are still in your '''vm2''' machine.#Test email from your machine by sending an email to your '''Seneca email account''' using the following command:<br>'''mail -s "PART C3" <Your Seneca email address>'''<br><br>:'''NOTE:''' after you type in your letter, enter a period in the first column on the last line and hit the ENTER key.<br><br>#Check your Seneca email account to see if you got the email (note that If it may take a <u>few minutes to arrive</u>worked, so you may also wish to try an alternate email account if you have one like gmail, etc). When you do receive this indicates that email make a note of the return address.#If you did not receive the mailpostfix service is running, listening, check the mail logs on your vm2 machine to determine what the error is.#Test email from your Host Machine by sending an email to your Seneca account using the following command:<br>'''mail -s "PART C4" -r hacker@evil.com <Your Seneca email address>'''<br><br>#Check your Seneca email to see if you got the email. If you did make a note of the return address.#Repeat the steps for INSTALL &amp; '''SETUP THE MAIL TRANSFER AGENT (MTA)''' and '''INSTALL &amp; SETUP THE MAIL USER AGENT (MUA)''' for your '''VM3''' and test by sending e-mail messages responding to your vm2 and Seneca e-mail accountconnections.

<ol><li value===Testing email using IP Addresses==="4">Let's see if it works from other machines. Use '''nc''' to connect to '''vm2''' from '''vm3''' and see if it works. If your firewall is set up properly, the nc command should not permit a connection (i.e. ''no route to host'').</li><li>Create an iptables rule to allow incoming connections to your '''SMTP''' server on your '''vm2'''.</li><li>Once you open the port in the firewall, retry the '''nc''' command. You should get a different error this time (e.g. ''connection refused''). This time the problem is that your service isn't listening on the outside interface, it's currently configured to listen only on the loopback (lo) interface.</li><li>Make sure the new iptables rule gets saved so that it will be loaded automatically from startup.</li></ol>

'''Perform We need to configure the following Steps:'''MTA not only to listen to connections from other (separate) MTAs, but to set the domain name and server name in order to allow the user to issue emails in the "standard way", and allow mail messages to provide a correct email address for replies.

#Adjust your firewall (iptables) to allow traffic to '''port 25''' on both VMs.# Check your '''/var/log/maillog''' file to see Perform the log entries get created when mail is sent and received, or notes when something goes wrong.#Try sending an email from '''vm2''' to your '''vm3''' by issuing the commandfollowing steps:<br>'''mail -s "PART E2" yyyyyy@[192.168.X.4]'''<br><br>#Try sending an email from your '''vm3''' to '''vm2''' by issuing the command:<br>'''mail -s "PART E3" root@[192.168.X.3]''' <br><br>

# In your '''vm2''' machine, launch in editing session for the postfix configuration file called: '''/etc/postfix/main.cf'''# Our first editing change to the Postfix configuration will be to make the service "listen" for incoming connections on the external interface (i.e '''eth0''' from the VMs point of view).<br>Change the value of the following parameter to what is displayed below:<br><source>inet_interfaces =all</source># We should also set the string that will end up in the '''From:''' header in messages sent by this server.<br>Change the '''mydomain''' option to YOUR domain name (shown below):<source>mydomain =yoursenecaid.ops</source># Also you must set the '''hostname''' for this server so that will correctly specify the hostname in the '''From:''' header in a sent mail message.<br>Make certain the following parameter only appears once (shown below):<source>myorigin =$myhostname</source>#Ensure that your '''hostname''' and '''DOMAIN''' name is properly set on your machine, otherwise you will need to set the '''myhostname''' parameter.<br>{{Admon/important|Warning|Make sure there are no other un-commented copies of those above-mentioned parameters in the Postfix configuration file.}}<br><ol><li value="6">Restart the postfix service, then use the '''ss''' command to confirm that the your MTA is now listening on <u>all</u> interfaces (not just loopback)</li><li>Test email by connecting to it (using host names===the '''nc''' command) from your '''vm3''' machine.</li></ol>

Let's complete this ''Record steps, commands, and your observations in INVESTIGATION 2 in your OPS335 lab by sending email messages using our recentlylog-created domain name:book'''

'''Perform the following Steps==INVESTIGATION 3:'''SENDING EMAIL BETWEEN MTAs for vm2 and vm3 (NO ENCRYPTION)==

#Use the Your '''hostvm2''' and '''hostname''' commands to confirm that each server should now be capable of your machines has the same ''hostname'' and that the DNS service verifies this to be true.#Restart your MTA (postfix) server if you changed the hostname on either mail server.#Try sending mail to yourself on both machines. For example, as the username <senecaID> on VM 3, use the command:<br>'''mail <senecaID>@vm2.<yourdomain>.org'''<br><br>and '''NOTE:receiving''' the machine will prompt for a subject: enter "testing" without the quotes.<br><br>#Enter the body of your e-mail message. When you have completed entering your email message, enter a period (.) in column 1 on the last line of your letter. This will send the signal: '''end-of-filebut we can''' and your letter will t be mailedcertain until we test it. You should end up back at This also would not help the shell prompt. If you make a mistake, use '''CTRL-C''' to cancel users on the email (DO <u>NOT</u> USE CTRL-Z).#Use the '''mailq''' command on both other machines (you will need to be root) to view in the mail queue. Why would this command be useful for an administrator?#Use the mail command to check to see if you have received any mailnetwork, which are still not capable of receiving email.

'''Record Perform the following steps, commands, and your observations in INVESTIGATION 2 in your OPS335 lab log-book:'''

#What did changing Briefly list the steps to install the relay_domains parameter do?MUA on your server for text-based messaging.#What firewall rule or rules, Briefly list the steps to trouble-shoot your server if any, did you have could not send e-mail messages from your vm2 machine to an external e-mail server.#Write the command to send an e-mail message from your vm2 to enter so that email between your VMs would work?Seneca College e-mail account.#What is are the commands to issue in the mail prompt to:<ul><li>Read the first e-mail message displayed</li><li>Save the 4th e-mail message to the meaning of file pathname: ~/maildir/3.msg.txt</li><li>Delete the square brackets surrounding 3rd e-mail message displayed</li><li>Exit the IP address in mail command prompt and return to the examples?shell</li></ul>#What were the results of sending email between the VMsemails locally on your vm2 machine? Show log segments to verify your answers.# What is the purpose of an MTA?# What is the purpose of an MUA?# Draw a simple diagram showing how an MUA and an MTA are used to send e-mail messages between different servers.# List the steps to test a running postfix service using the nc application.