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OPS335 Lab 4

1,958 bytes added, 4 January
Sending a Mail Message from your vm2 Machine to your Seneca Email Account
[[Category:OPS335]][[Category:OPS335 Labs]]
{{Admon/important|Warning|Your lab 3 must be complete with a functioning DNS server for your domain before this lab will work.}}
Online References:You may not be aware of it as an user, but email is a very <u>complex</u> system to administer. In fact, the more modern e-mail systems (eg. web-based mail applications, etc) are more technically involved than the other archaic, hard-to-configure, and sometimes inter-operable mail systems.
* [ OPS335 Mail Server Notes ] (Course Notes providing Mail Server Concepts)* [ are going to-send-spread the remaining email-from-labs over a few weeks, so that by the-linux-command-line/ Mail Send Command] (examples how end of this topic, you will have a sufficient understanding of what services are involved in sending, filtering, and reading email. You will also have the skills to send e-configure a basic mail setup using mail command)* [ default services provided for your Centos7 Linux distribution.html#prompt_commands View and Manage Received e-mail Mesages] (Common commands to view and manage received email messages)* [ Reading Full Email Headers] (Explanation of message header information)
Believe it or not, this is a simple diagram of you sending an email to someone else:
==OVERVIEW &amp; PREPARATION==This lab will show you how to set up a Mail User Agent ('''mailx''' package) on your '''VM2''' machine to allow users of that VM to send and receive e-mails locally on your VM2 machine, and to send a text-based e-mail to your Seneca mail account (only to send to an external server, but not receive). You will also learn which Mail Transfer Agent (MTA) is allowing messages to be sent locally in your VM2 and externally to your Seneca College account. You will also learn where the message store (MS) is located, and how messages can be saved to other folders. In order to send e-mail messages '''between your different VMs, a more complex set-up is required''', and will be addressed in the second part of lab4. The '''diagram''' below shows the layout of the what this lab should be able to accomplish:  [[Image:email-setupEmail-simpleservers.png]]
This lab will show you how to set up a Mail User Agent ('''MUA'''), using the '''mailx''' package on your '''vm2''' machine to send and receive e-mails on your local VM. In this case, the '''Postfix''' package which represents your '''MTA''' 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 '''vm2 machine''' to your '''Seneca mail account'''. You will also learn how to 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 other folders.
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 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: [ complex diagram 1] , [ complex diagram 2].
===Online References:===
* [ Mail Send Command] (examples how to send e-mail using mail command)
* [ View and Manage Received e-mail Mesages] (Common commands to view and manage received email messages)
* [ Reading Full Email Headers] (Explanation of message header information)
* [ Here's an overview] (common mail server terms)
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''' vm2''' machine and to '''only send ''' mail messages from your '''vm2''' machine to your Seneca e-mail account'''.
'''NOTE:''' Due Because you're using private IP addresses and no external DNS servers are pointing to the simplicity of this mail server setup, and the setup of Seneca College's mail serveryour network, you '''<u>cannot</u>''' send Seneca e-mail messages from outside your environment to your '''VM2vm2''' 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> [ Mail Send Command Examples]
===Sending a Mail Message from your VM2 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. If it doesn't work for you: don't worry about it for lab submission purposes.}}
We will now test to see if your MTA for your VM2 vm2 machine is correctly running by sending email messages from your VM2 vm2 machine to your Seneca e-mail account.
'''Perform the following steps:'''
#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, type period "." and then press the ENTER key combination '''&lt;ctrl&gt;&lt;d&gt;''' 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.
#Test Once you have succeeded in sending the first email from your '''Host Machine''' by sending an , send a second email to your Seneca account the same destination using the following command:<br>'''mail -r " (Canadian Revenue Agency)" -s "Lab4a - test2" <Your Seneca email address>#Check your Seneca 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?
===Sending a Mail Message within your VM2 vm2 Machine (vm2)===
We will now test both your MUA (mailx) and MTA (postfix) by sending and receiving e-mail messages on the local VM2 vm2 machine only.
'''Perform the following Steps:'''
#Send an email message locally (i.e. only within) your VM2 vm2 machine ) by issuing the command:<br>'''mail -s "Lab4a - Local - Test1" <yourSenecaID>'''
#After you type in the body of the mail message, move to an empty line, type period "." and press the ENTER key to send the message.
# Issue the following command: Login with your '''cat /var/log/spool/mail/<yourSenecaID>regular user'''<br>What do you see? What does this show you in terms of where mail is stored on your e-mail server?#Issue and issue the following command to read the mail message you send to yourself:<br>'''mail'''<br><br>'''NOTE:''' You can refer to the link below to view a reference chart on how to read and delete received e-mail messages at the mail command prompt:<br>[ Commands to View and Manage Received e-mail Mesages]<br><br>#Issue the following command: '''cat /var/spool/mail/<yourSenecaID>'''<br>What do you see? What does this show you in terms of where mail is stored on your e-mail server?#If you received an e-mail message, the message and subject line should appear as a listing in your mail command.<br><br>'''NOTE:''' If you did not receive a mail message, check your mail server settings, check to see if you your mail server is running and also check '''/var/log/maillog''' and '''/var/log/messages'''(this step requires '''root''' privilege).<br><br>#Type Once you have received the message, type the mail message number that is displayed in your e-mail message list in the prompt and press ENTER. You should be able to confirm the message body that you sent.
#Exit the mail program by typing the letter '''q''' and press ENTER.
#Re-issue the '''mail''' command. What happened? Issue the command: '''cat /var/spool/mail/<yourSenecaID>'''. What do you notice?
#Exit the mail command.
===Checking the Message Store (MS) of Received Mail Messages===
We will now view the Message Store where messages are sent to be retrieved from the mail program.<br>We will also show you how to save mail messages into another message store file in another directory.
'''Perform the following Steps:'''
#Create a directory in your home directory called: '''mail'''.
#Re-issue the '''mail''' command, and enter the following command at the mail prompt: '''save &nbsp; 1 &nbsp; mail/msg1'''<br>Use the cat command to check the contents of '''/var/spool/mail<yourSenecaID>''' and '''~/mail/msg1'''. Exit the mail command.
#Try sending another e-mail from your VM2 account to yourself, but using your first name instead by issuing the following command:<br>'''mail -s "Lab4a - Local - Test2" <yourFirstName>'''
#Issue the '''mailq''' command on your VM2 machine (you will need to be root) to view the mail queue. Why would this command be useful for an administrator?
#Now, issue the '''mail''' command to see if you received that e-mail message. Did it work? If so, why?<br>Record your observations in your OPS335 lab logbook.<br><br>
'''Record steps, commands, and your observations in INVESTIGATION 1 in your OPS335 lab log-book'''
==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: IDENTIFYING A DEFAULT MAIL TRANSFER AGENT * Individuals outside of your domain will never find the MX records because there are no other DNS servers pointing to your DNS server (i.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 '''MTAprivate subnet''')==, which is not routeable on the Internet, so it cannot be reached from outside of your system.
Obviously === Verify the Mail Transfer Agent must be running in order to send e-mail messages locally or to external mail server (like In this section, we will determine information relating to Seneca College's MTA when email messages are sent via your VM2 machine.Postfix Service Status ===
=== Email Headers ==='''Perform the following steps:'''
Normally, email headers are seldom seen with our e-mail applications such as #The '''MS Outlookpostfix''' (webmail) or '''Thunderbird''application should be installed by default. If it isn't, install it. There are way in order to view detailed header information for each #Postfix is capable of sending email we send with the default configuration, so start and enable this service, and verify that provides information how the email message was sent, including postfix service is running.#Look for the running postfix service in the name list of listening ports by issuing the program that following command:<br><source>ss -atnp</source>#Which service is postfix running as ? Locate the Mail Transfer Agent port used by SMTP, and its IPADDR. Although these email headers may look complicated, they can trace the steps of sending for connections with the state LISTEN (i.e-mail messages among the MTAs to gain a better understanding of the email transmission process. currently listening).#Write your observations in your lab logbook.
=== Testing the connection to the Postfix Service ===
We will be demonstrating the use of the '''Perform the following Steps:nc'''application to test that the postfix service is running and listening.
{| width="40%" align="right" cellpadding="10"'''Perform the following steps:'''
|- valign="top"|[[Image:outlook-lite-mode.png|thumb|right|300px|# If your MS outlook web application looks like above, then your MS Outlook application is using the '''lite versionnc'''command is not installed on your vm2 machine, and you would have to switch versions install it (see below install '''nc''' command for procedureyour '''vm3''' as well). ]]|# Connect from your '''vm2''' to itself using the '''nc''' command by issuing the following command:<br><source >nc localhost 25</source>[[Image# You should see a response:outlook-regular-mode<br><source >220 vm2.yourdomain.png|thumb|right|300px|If your MS outlook web application looks like aboveops ESMTP Postfix</source># You could theoretically use SMTP commands to send an email here, then but this would be a very unusual use of your MS Outlook application is using mail server. You have an '''MUA''' for a reason.#Enter the command '''standard versionQUIT'''to close the connection to the server, so you can skip then '''<ctrl>-c''' to terminate the procedure to switch versionsnc command.]]|}
#Make certain you are in your '''vm2''' machine.#Send another email message from your VM2 machine to your '''Seneca email account''' using the command:<br>'''mail -s "Lab4a - Header Message" <Your Seneca email address>'''<br><br>:'''NOTE:''' after you type in the body of If it worked, this indicates that the mail messagepostfix service is running, move to an empty linelistening, type period "." and press the ENTER key responding to send the message.<br><br>#View your e-mail message in your Seneca email accountconnections.
<ol><li value="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>
'''Switching Modes in MS Outlook Web Application:'''=== Listening on all interfaces ===
[[Image:option-lite.png|thumb|right|400px|How We need to configure the MTA not only to listen to switch connections from other (separate) MTAs, but to '''standard version''': click set the domain name and server name in order to allow the user to un-check issue emails in the ''lite version'' option "standard way", and save option settingallow mail messages to provide a correct email address for replies. ]]
'''Perform the following steps:If you are using web-mail to read your Seneca e-mail message, then your Mail User Agent is probably using the MS Outlook web application. In order to view mail header information in your MS Outlook web application, you need to be in a particular "viewing-mode".'''
# In your '''vm2''' machine, launch in editing session for the postfix configuration file called:This program can run in '''standard version/etc/postfix/''' or # Our first editing change to the Postfix configuration will be to make the service "listen" for incoming connections on the external interface (i.e '''lite versioneth0'''from the VMs point of view). If your MS Outlook web application <br>Change the value of the following parameter to what is using 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 '''"lite version"mydomain''', then it should look similar 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 left-most diagram following parameter only appears once (shown below):<source>myorigin = $myhostname</source>#Ensure that your '''hostname''' and '''DOMAIN''' name is properly set on the rightyour machine, and otherwise you should follow will need to set the procedure below to switch to '''"standard version"myhostname'''parameter. If your MS Outlook web application appears like <br>{{Admon/important|Warning|Make sure there are no other un-commented copies of those above-mentioned parameters in the right-most diagram on Postfix configuration file.}}<br><ol><li value="6">Restart the rightpostfix service, then use the '''ss''' command to confirm that the your program MTA is now listening on <u>all</u> interfaces (not just loopback)</li><li>Test by connecting to it (using the '''"standard version"nc''' command) from your '''vm3''', which mean that you can skip the procedure to switch versionsmachine.</li></ol>
:'''Procedure to Change from Lite-mode to Regular mode:''' :<ol type="a"><li>Click '''options''' located at the top-right corner of the MS Outlook web application window (to the left of the '''Sign Out''')</li><li>Click '''Outlook''' Version on the left-side of the ''Options'' window.</li><li>Click to de-select the '''Use the light version''' (i.e. no check mark)</li><li>Click the Save button near the top of the Options window to save your settings.</li><li>Sign-out of your MS Outlook SessionRecord steps, commands, and login again.<br><br>'''NOTE: If your MS Outlook application does not change versions, then close all of observations in INVESTIGATION 2 in your webOPS335 lab log-browsers, and then log into your Seneca email'''<br><br></li></ol>
=== Viewing Seneca Mail Message Headers =INVESTIGATION 3: SENDING EMAIL BETWEEN MTAs for vm2 and vm3 (NO ENCRYPTION)==
Now that you are using the standard version Your '''vm2''' server should now be capable of MS Outlook'''sending''' and '''receiving''' email, but we can't be certain until we will now analyse test it. This also would not help the users on the mail message header other machines in your Seneca e-mail account that was sent from your VM2 machine to obtain information regarding Seneca's Mail Transfer Agent (MTA)the network, which are still not capable of receiving email.
'''Perform the following steps:'''
{| width="40%" align="right" cellpadding="10"
|- valign="top"|[[Image:view-message-details.png|thumb|right|300px|# Repeat the configuration from investigation 2 on '''Right-clickvm3''' on the mail message (swap vm2 and vm3 when issuing command so that you recently sent with subject line "Lab4a - Header Message" are configuring vm3, and, select '''View Message Details'''. '''NOTE: If no mail message headers appear, try the previous step again until you see mail message header information.''' ]]|[[Image:message-details.png|thumb|right|300px|Use these header details using your vm2 server to analyse information regarding test the MTAs use to transfer the mail message from your VM2 machine to your Seneca mail accountconnections).]]|}#'''Right-click''' on the mail message Once that you recently sent with subject line "Lab4a - Header Message".#Within the context menuis complete, select send an email from '''View Message Detailsroot on vm2'''.<br><br>to '''NOTE: If no mail message headers appear, try the previous step again until you see mail message header information.root on vm3'''<br><br>#To make the header information easier to read, highlite the text, copy and paste into a text editor (like then reply '''geditfrom vm3 to vm2''').<br><br>#Locate the section for the MTA that was used to transfer the message from your VM2 machineIf both messages arrive, both MTAs are working. What program does that MTA If not, use? What is the IPADDR? Record your observations in your lab logbook.<br><br>#Locate the section for the MTA that was used troubleshooting tools and techniques you have already learned to receive diagnose and fix the e-mail message for your Seneca College e-mail. What program does that MTA use? What is the IPADDR? Are those two MTAs the same? Record your observations in your lab logbookproblem.<br><br>#Use either the {{Admon/important |Backup your VMs!|You MUST perform a '''nslookupfull backup''', of ALL of your VMs whenever you complete your '''hostOPS335 labs''', or when working on your '''digOPS335 assignments''' utilities to query those servers to see if you can obtain additional information regarding those servers.  === Resetting MS Outlook Web Application to Lite Version (If Required) === '''If your MS Outline web application was previously You should be using the lite versiondump or rsync command, and you wish to revert to this original setting, perform should use the following steps:''' #Click the '''settings''' icon (looks like a gear located left Bash shell script that you were adviced to the help (?) icon.#Click the General categories under the options on the left-side of the options menu.#Click Light Version, and create in the details area order to the right, make certain that the Use the light version backup all of Outlook on the web is selected (i.e. check mark appears), and click on Save at the topyour VMs.}}#Sign-out of your MS Outlook Session, and login again.<br><br>'''NOTE: If your MS Outlook application does not change versionsRecord steps, then close all of your web-browserscommands, and then your observations in INVESTIGATION 3 in your OPS335 lab log into your Seneca email account.-book'''
'''Record stepsUpon completion of this lab you should have postfix mail servers running on two machines, and starting automatically when they do. These servers must have sent email both ways between each other (from vm2 to vm3, commandsand from vm3 to vm2), and to your observations in INVESTIGATION 2 in your OPS335 lab log-book'''seneca email (or other external mail server).
===Online Submission===
Follow the instructions for lab 4a on blackboard.
===Andrew's sections===
==COMPLETING THE LAB==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.
Arrange proof that You'll get the same grade regardless of how you can send e-mail from your '''VM2''' machine choose to submit your '''Seneca College e-mail account''', and than you can '''send and receive e-mail messages locally on your VM2 machine only'''. Also show your logbook notes regarding MTA information from your sent email header on your Seneca College mail accountwork.
::<span style="color:green;font-size:1.5em;">&#x2713;</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;">&#x2713;</span>Download and run '''''' on your '''host''' machine.
::<span style="color:green;font-size:1.5em;">&#x2713;</span>Completed Lab4a log-book notes.
#Briefly list the students steps to install the MUA on your server for text-based messaging.#Briefly list the steps to trouble-shoot your server if you could not send e-mail messages from your VM2 vm2 machine to an external e-mail server.#Write the command to send an e-mail message from your VM2 vm2 to your Seneca College e-mail account.#What 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 file pathname: ~/maildir/3.msg.txt</li><li>Delete the 3rd e-mail message displayed</li><li>Exit the mail command prompt and return to the shell</li></ul><br>#What were the results of sending emails locally on your VM2 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 show your email header to trace test a running postfix service using the transmission between Mail Transfer Agents among different mail serversnc application.

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