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[[Image:email-setup-simple.png]]
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 you to go into tremendous depth (just the 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 is its main purpose, as opposed to the following: [https://en.wikipedia.org/wiki/Postfix_%28software%29#Architecture complex diagram 1] , [https://www.credativ.de/blog/postfix-architecture-overview complex diagram 2].
===Online References:===
We will be using a simple text-based '''Mail User Agent (MUA)''' 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.
'''NOTE:''' Due to the simplicity of this mail server setup Because you're using private IP addresses and the lack of other no external DNS servers are pointing to your network, and the setup of Seneca College's mail server, you '''<u>cannot</u>''' send Seneca e-mail messages from outside your environment to your '''vm2''' machine.
=== Installing the Mail User Agent (MUA)===
#Make certain you are in your '''vm2''' machine.
#Issue the following command to install Install the '''mailx''' application (MUA):<br>'''using yum install mailx'''<br><br>
:'''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]
===Sending a Mail Message from your vm2 Machine to your Seneca Email Account===
{{Admon/important|Note|These instructions no longer work reliably. You can still send email to your own email server, and look at the server logs to see that it did really get sent. But it probably won't be accepted for one of a multitude of good reasons.}}
We will now test to see if your MTA for your vm2 machine is correctly running by sending email messages from your vm2 machine to your Seneca e-mail account.
#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 "Lab4a - test1" <Your Seneca email address>'''<br><br>'''NOTE:''' after you type in the body of the mail message, move to an empty line, and then press the key combination '''<ctrl><d>''' to send the message.<br><br>
#Check your Seneca email account (Inbox / Junk Email Folder) to see if you got the email (note that it may take a <u>few minutes to arrive</u>, so you may also wish to try an alternate email account if you have one like gmail, etc). When you do receive that email, make a note of the return address.
#If you did not receive the mail, check the mail logs on your vm2 machine to determine any errors messages that would indicate a mail server setup problem.
#Once you have succeeded in sending the first email, send a second email to the same destination using the following command:<br>'''mail -r "someone@hacker.com (Canadian Revenue Agency)" -s "Lab4a - test2" <Your Seneca email address>
#Check your email to see if you got the email. If you did, make a note of the return address. How would you think that including the '''-r''' 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 help prevent this type of attack from happening?
#The '''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 command:<br><source lang="bash">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.
# If the '''nc''' 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 command:<br><source lang="bash">nc localhost 25</source># You should see a response: <br><source lang="bash">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.
# 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 lang="bash">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 lang="bash">mydomain = yoursenecaid.ops</source># Also you must set the '''hostname''' for this server so that will correctly specify the hostname in the '''From:''' head in a sent mail message.<br>Make certain the following parameter only appears once (shown below):<source lang="bash">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>
===Online Submission (Peter Callaghan's Classes only)===
Follow the instructions for lab 4a on moodleblackboard. ===Andrew's sections=== You may choose to:* Submit screenshots of your work on Blackboard, in which case you don't need to come to the lab.* Or come to the lab, show me your work, and talk to me about it. I want to hear what you've learned and answer any questions you have. You'll get the same grade regardless of how you choose to submit your work.
::<span style="color:green;font-size:1.5em;">✓</span>Arrange proof that you can send e-mail from your '''vm2''' machine to your '''Seneca College e-mail account''', and than you can '''send and receive e-mail messages between on your vm2 and vm3 machines'''.
::<span style="color:green;font-size:1.5em;">✓</span>Download the labcheck4a.bash checking bash shell script by issuing the command:<br><br>and run '''wget httphttps://matrixict.senecac.onsenecacollege.ca/~peterandrew.callaghansmith/files/OPS335ops335/labcheck4a.bash'''<br><br>set execute permission and run the shell script on your '''host''' machine. ::*For '''Peter's classes''', follow his Online Submission instructions in Moodle.::*For '''Murray's classes''', run command (piping to the '''more''' command) on both VM2 and VM3 and show output to instructor.
::<span style="color:green;font-size:1.5em;">✓</span>Completed Lab4a log-book notes.
