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==MAIL SERVER RESOURCESOVERVIEW & PREPARATION==

* [https://prezi.com/iuk-advzak_o/mail-servers-postfix/ OPS335 Mail Server Notes ] Course Notes providing Concepts We are going to spread the remaining email labs over a few weeks, so that by the end of this topic, you will have a sufficient understanding of what services are involved in sending, filtering, and Overview of mail server setup* [http://www.simplehelpreading email.net/2008/12/01/how-to-send-email-from-You will also have the-linux-command-line/ Mail Send Command] (examples how skills to send e-configure a basic mail setup using mail command)* [http://www.johnkerl.org/doc/mail-how-tothe 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)* [https://support.google.com/mail/answer/29436?hl=en Reading Full Email Headers] (Explanation of message header information)

==OVERVIEW & 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[[Image:Email-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 foldersservers.png]]

In order 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-mail messages mails on your local VM. In this case, the '''Postfix'''between package which represents your different VMs'''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 more complex settext-based e-up is requiredmail 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, and you will be addressed in learn where the second part of lab4message store (MS) is located that stores mail messages until they are viewed and either deleted or transferred to other 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] , [Imagehttps:email//www.credativ.de/blog/postfix-setuparchitecture-simpleoverview complex diagram 2].png]]

==INVESTIGATION 1: INSTALL, SET-UP, AND USE THE MAIL USER AGENT ('''mailxNOTE:'''Because you' Package)== We will be re using a simple text-based Mail User Agent ('''MUA''') called '''mailx''' in this lab to '''send and receive mail messages within your VM2 machine''' private IP addresses and to '''send mail messages no external DNS servers are pointing to your Seneca e-mail account'''. '''NOTE:''' Due to the simplicity of this mail server setup, and the setup of Seneca College's mail servernetwork, you '''<u>cannot</u>''' send Seneca e-mail messages from outside your environment to your '''VM2vm2''' machine.

#Issue the following command to install Install the '''mailx''' application (MUA):<br>'''using yum install mailx'''<br><br>

===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.

#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.

#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 "someone@hacker.com (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.

#Send an email message locally (i.e. only within) your VM2 vm2 machine ) by issuing the command:<br>'''mail -s "Lab4a - Local - Test1" <yourSenecaID>'''

# 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>[http://www.johnkerl.org/doc/mail-how-to.html#prompt_commands 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.

#Re-issue the '''mail''' command. What happened? Issue the command: '''cat /var/spool/mail/<yourSenecaID>'''. What do you notice?

'''Record steps, commands, and your observations in INVESTIGATION 1 in your OPS335 lab log-book''' ===Checking the Message Store INVESTIGATION 2: SETUP MTA TO SEND MAIL MESSAGES (MSNO ENCRYPTION) of Received Mail Messages===

We will now view be using the '''Postfix''' application as the Message Store where messages are sent to '''MTA''', and we will be retrieved from setting it up on your '''vm2''' and '''vm3''' machines. They will act as the mail program"sending" email servers for your internal network. We You will also show be able to send email out of your network, and receive email from within your network, but you how will '''<u>not</u>''' receive email from outside of your network due to save mail messages into another message store file in another directorythe following reasons:* 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 '''private subnet''', which is not routeable on the Internet, so it cannot be reached from outside of your system.

'''Perform === Verify the following Steps:'''Postfix Service Status ===

#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 Perform the following commandsteps:<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>

#The '''Record stepspostfix''' application should be installed by default. If it isn't, install it.#Postfix is capable of sending email with the default configuration, commandsso 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>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 INVESTIGATION 1 in your OPS335 lab log-book'''logbook.

Obviously '''Perform the Mail Transfer Agent must be running in order to send e-mail messages locally or to external mail server (like myseneca.ca). In this section, we will determine information relating to Seneca Collegefollowing steps:'''s MTA when email messages are sent via your VM2 machine.

Normally::'''NOTE:''' If it worked, email headers are seldom seen with our e-mail applications such as web-mail, MS Outlook, or Thunderbird. There are way in order to view detailed header information for each email we send this indicates that provides information how the email message was sent, including the name of the program that postfix service is running as the Mail Transfer Agent , listening, and its IPADDR. Although these email headers may look complicated, they can trace the steps of sending the e-mail messages among the MTAs responding to gain a better understanding of the email transmission processconnections.

<ol><li value="4">Let's see if it works from other machines. Use '''nc''' to connect to '''vm2'''Perform the following Steps:from '''vm3'''[[Image:outlook-lite-modeand see if it works.png|thumb|right|100px|If your MS outlook application looks like above, then your MS Outlook application firewall is in lite-modeset up properly, and needs the nc command should not permit a connection (i.e. ''no route to be changed to regular-modehost''). ]]</li>#Make certain you are in <li>Create an iptables rule to allow incoming connections to your '''vm2SMTP''' machine.#Send another email message from your VM2 machine to server on your '''Seneca email accountvm2''' using the command:.<br/li>'''mail -s "Lab4a - Header Message" <Your Seneca email addressli>Once you open the port in the firewall, retry the '''<br><br>nc'''NOTE:command. You should get a different error this time (e.g. ''connection refused' after you type in '). This time the body of problem is that your service isn't listening on the mail messageoutside interface, move it's currently configured to an empty line, type period "listen only on the loopback (lo) interface." and press </li><li>Make sure the ENTER key to send the messagenew iptables rule gets saved so that it will be loaded automatically from startup.<br/li><br/ol>#View your e-mail message in your Seneca email account.

'''NOTE:''':If you are using web-mail to read your Seneca e-mail message, then your Mail User Agent is probably using the MS Outlook program. This program can run in regular-mode or lite-mode. If it runs in lite-mode, the email should appear === Listening on the left-most image displayed to the right. If it appears that your MS Outlook program is using regular-mode, then you can skip the procedure to switch from lite-mode to regular-mode.all interfaces ===

:'''To switch We need to configure the MTA not only to listen to connections from lite-mode other (separate) MTAs, but to set the domain name and server name in order to allow the user to regular modeissue emails in the "standard way", perform the following steps:'''and allow mail messages to provide a correct email address for replies.

'''Perform the following steps:<ol type="a"><li>x</li><li>x</li><li>x</li></ol>'''

Arrange proof that Upon completion of this lab you can send e-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, and from vm3 to vm2), and to your seneca email (or other external mail server).  ===Online Submission===Follow the instructions for lab 4a on blackboard.<!--===Andrew's sections=== You may choose to:* Submit screenshots of your work on Blackboard, in which case you don''VM2''' machine t need to come to the lab.* Or come to the lab, show me your '''Seneca College e-mail account'''work, and than talk to me about it. I want to hear what you can 've learned and answer any questions you have. You''send and receive e-mail messages locally on ll get the same grade regardless of how you choose to submit your VM2 machine only'''work.

#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.