[[Category:OPS335]][[Category:OPS335 Labs]] = Email Servers =OVERVIEW=={{Admon/important|Warning|Your lab 4a must be complete before you can start this lab.}} In Lab 4a, you configured and ran the '''Postfix''' application for our MTA (a.k.a. SMTP server) on your '''vm2''' and '''vm3''' machines.
You may not That setup has some major drawbacks::* It required an SMTP server ('''MTA''') to be configured on each machine.:* The Message Store ('''MS''') would also be aware of it as unique to each machine - what a user but email is a very complex system to administer, in fact it's a very complex system of received on one server would not exist on any other archaic, hard-to-configure, sometimes-interoperable complex systems.
We're going to spend three weeks working on it In this lab you will centralize some of this information, so that by the end of the course you will have a general understanding of what services are involved user can send email from any machine in sending, filteringthe network, and reading email. You will also have the skills incoming mail sent to configure a basic setup using the default services on CentOS 7centralized messages store.
== Overview =='''The a diagram below (duplicate to lab 4a) shows your basic setup of your email system:'''
This is a simple (yeah, really) diagram of how you can send an email to someone else:
[[Image:Email-servers.png]]
You will begin by modifying the existing '''Postfix''' ('''MTA''') servers to make mail they send come from your domain (instead of each machine). Then you will add a record to your DNS server to allow mail to be sent to the domain itself, instead of the individual machines. Next, you will add a Local Delivery Agent ('''LDA''') to your '''vm3''' by installing '''dovecot-lda''', configure it, and test it to make sure that is is working correctly. Finally, you will set up an '''IMAP''' server called '''Dovecot''' on your '''vm3''' machine, so you can read your email from an MUA such as ''Thunderbird'' or a ''Webmail'' application. You will set up a webmail application called '''Roundcube''' in a later lab). === Learning About the Services Involved in an Email Delivery === In reality, the terms '''MTA''', '''MDA''', '''MUA''', '''LDA''' can actually be considered misleading since some of those services can be combined together to form a single entity (application), while other applications may operate as separate entities. There may be overlap, so if you don't find those acronyms helpful, don't worry too much about them. On the other hand, when referred to in diagrams, they can help to visualize those processes when trying to understand how an e-mail system works. [http://wiki.dovecot.org/MailServerOverview Here is an overview] of those terms (from the Dovecot wiki). It is worth viewing this link. In the diagram displayed above, the elements include: * '''User Account'''. The individual who wants to send or receive mail messages.* '''MUA''' (email client). This is the application that the individual uses to send or receive mail messages. It can be a '''native application''' or a '''web application'''. You will learn how to setup and use both types of these applications throughout the remainder of this course.* Two '''MTA''' servers. These are the servers responsible for getting your emails to the <u>destination</u> server.** They are similar to routers (which route packets) but work on the <u>application</u> layer rather than the <u>network</u> layer.** In our example, there are only two MTAs - but there can be several.** You connect to your MTA over a <u>secure</u> connection, so your emails can't be read by the operators of the network you're connected to.** The mail message then travels the rest of the way to the destination MTA <u>unencrypted</u>, so anyone with access to the routers in-between can read all your emails. That is why many organizations will refuse to send you confidential information over email.* '''LDA/MDA''' Server. This server will receive the email from the MTA, and will store it on disk in some format. '''MailDir''' and '''MBOX''' are the most popular mailbox formats.* '''IMAP/POP3''' server(s). When sending an email, you send it to the destination using your MTA, but you also want to save it in your '''"Sent"''' folder for yourself. This is accomplished by a separate connection to either your '''IMAP''' or '''POP3''' server.** Thus, a situation can occur that although you sent your email successfully, it may never make it to your "Sent" folder - the <u>second</u> connection to your IMAP server is quite unrelated to the first connection to the '''SMTP''' server.* '''DNS''' Server. A DNS server is also involved - it is needed to retrieve the address of the email server responsible for email for a particular domain. This is done with '''MX''' records. ===Online References=== * [Categoryhttps:OPS335//help.ubuntu.com/community/Dovecot Dovecot Community Documentation]* [http://wiki.dovecot.org/LDA Dovecot-lda]* [http://wiki.dovecot.org/LDA/Postfix Configuring dovecot-lda with postfix] == INVESTIGATION 1: INSTALL THUNDERBIRD (MUA) and SETUP A REFERENCE CLIENT== Unlike the '''mailx''' (MUA) application you installed and used in Lab 4a, this lab will be using the '''Thunderbird''' (MUA) application instead which is a graphical application that uses a '''centralized Message Store''' (MS) to retrieve and read mail messages. Although we will be eventually setting up the Thunderbird application to perform all the mail operations discussed above, you need to learn to '''"walk before you can run"'''. Eventually, you are going to set up all those mail services, but to begin with, you will set up an email client to connect to an already working server which is the '''Seneca email server'''. Once we learn how to do this for our Seneca email account, then we can use it for our mail servers for our VM2 and VM3. '''Perform the following steps:''' #Switch to your '''host''' machine, and install the '''Thunderbird''' email application.#When you first launch the Thunderbird application, a configuration dialog should appear as shown in the diagram below: <br>::[Category[Image:OPS335 LabsSeneca-student-thunderbird-email-setup.png|600px]]<br><ol><li value="3">Use the data in the table below to configure the Thunderbird settings dialog box for YOUR Seneca e-mail account:</li></ol> {| class="wikitable" border="1" style="margin-left:40px;"! Setting !! '''Incoming: IMAP''' !! '''Outgoing: SMTP'''|-| '''Username'''|| yoursenecauserid@myseneca.ca || yoursenecauserid@myseneca.ca|-| '''servername''' || outlook.office365.com || outlook.office365.com|-| '''port''' || 993 || 587|-| '''security''' || SSL/TLS || STARTTLS|-| '''References''' | colspan="2" | [1] [https://employees.senecacollege.ca/spaces/77/it-services/wiki/view/2394/other-email-clients ITS - Configuring other Email Clients]|} ::Note that your username is your full email address(<em>yourid@myseneca.ca</em>) and not just <em>yourid</em>. {{Admon/important |Unencrypted Options|Notice that there are <u>unencrypted</u> options available to connect to your SMTP/IMAP servers but those are rarely used these days - the potential for abuse is too great. On a free wifi network, the operator would be able to not only read your email, but also obtain your password without any password/encryption cracking tools. In fact, even on a private wired network, it is not uncommon for an employer to use a packet sniffer utility to monitor all the traffic going over their network (Packet Sniffing applications were actually found to be legally acceptable practice if used by the management of organizations)}}<br><ol><li value="3">After you create your '''Thunderbird''' account, you should be able to read your existing email and send new email within the Thunderbird application.</li><li>Take time to view your ''Account Settings'' and ''Preferences'' to get a feel for what settings exist. For example:<ul><li>How often will Thunderbird check for new messages?</li><li>Will the messages you write be in HTML or plain text?</li><li>How do you change your SMTP server settings? Why are they in a different section?</li></ul></li><li>The main objective of this section was to learn how to setup your Thunderbird application to read your Seneca email, so in the next section you can use the exact type of setup for your own email server.</li></ol> '''Record steps, commands, and your observations in INVESTIGATION 1 in your OPS335 lab log-book''' == INVESTIGATION 2: SETUP A CENTRALIZED MESSAGE STORE == === Setup Your MTA to Use Correct Domain=== In Lab 4a, both of your email servers were sending mail messages addressed from users of the actual machines themselves. This would be confusing for the receiver who might get emails from the same user @vm1, vm2, and vm3. Which would they respond to? To avoid this problem from occurring, we can make all servers make the sent mail appear to come from a central location (usually the '''domain'''), and make incoming email sent to that address to be accessible from machines within our network. '''Perform the following steps:''' # Issue the '''mail''' command to view the email messages you sent between your '''vm2''' and '''vm3''' in your lab 4a. Notice that each is addressed from root on whichever machine sent it.# On both machines (vm2 and vm3), edit the '''/etc/postfix/main.cf''' file to change the '''myorigin''' parameter from '''$myhostname''' to '''$mydomain'''. Restart the '''postfix''' service.# Now, send emails messages (via the '''mail''' command) between both of your vm2 and vm3 machines, and view the mail messages by issuing '''mail''' in each vm. The sender address should now read that the received mail messages came from '''root@yourdomain.ops'''. ::The next step is to configure what addresses that the server will receive email for. This is done using postfix by setting the '''mydestination''' parameter (configuration variable) to include '''$mydomain''' (this is assuming you've set up '''mydomain''', '''myorigin''' , and '''inet_interfaces''' properly). <ol><li value="4">Edit the '''/etc/postfix/main.cf''' file for '''vm3 ONLY''', scroll down to the line containing: '''mydestination''' and change line to the text shown below:<br><source>mydestination = $mydomain, $myhostname, localhost.$mydomain, localhost</source>'''Note:''' Even though your machine's name is ''vm3.yoursenecaid.ops'', your postfix MTA will also receive emails addressed to the domain called: yoursenecaid.ops</li></ol><br>::In order for this to work, we need to add a DNS record that will point mail sent to the domain towards one of the SMTP servers configured to accept it. <ol><li value="5">Add an '''MX''' record to the forward lookup zone on '''host''' so that all incoming mail addressed to the domain is sent to your vm3.</li><li>Restart the service and use the '''dig''' command to confirm that it works.</li><li>Send an email from your '''vm2''' to '''root@yourdomain.ops'''</li><li>Confirm that it arrives on your '''vm3''' machine</li></ol> === Relay Email Through Another Server=== When email is sent from either vm, it is addressed from the domain, but receiving MTAs might query why mail sent from vm2 doesn't match the address of the MX record for the domain. This would be a red-flag for potential spam. To avoid this, we can relay all mail sent from vm2 (or any other machine in our network) through vm3 so that it properly appears to come from the mail server that matches the MX record for the domain. '''Perform the following steps:''' # Move to your vm2 machine.# Direct your '''vm2''' MTA to relay mail through vm3, by making the following editing change for the '''/etc/postfix/main.cf''' file:<br><source>relayhost = vm3.<yourdomain>.ops</source># Restart the '''postfix''' service.# Next, you must instruct your '''vm3''' machine to allow your vm2 machine to pass email through it by making the following editing change to the '''/etc/postfix/main.cf''' file:<br><source>mynetworks = 192.168.X.0/24</source>NOTE: Substitute in your '''own network''' for X<br><br># Restart the '''postfix''' service. All mail is now being delivered to a centralized location (and also appears to be coming from that same location), but a user would still have to access that server to retrieve it. === Install and Configure the Local Delivery Agent (LDA/MDA) === Postfix is capable of performing the function of an LDA, but its LDA capabilities are limited, thus postfix is generally not used for that purpose. Currently, the most popular LDA is ''LMTP'', but we will be installing, configuring, and using an LDA called '''Dovecot''' since it is also popular and we will setting up Dovecot as an '''IMAP''' server later in this lab. Using both Postfix and Dovecot will actually increase the performance of our IMAP server. '''Perform the following steps:''' #Move to your '''vm3''' machine.#Dovecot is not installed when you installed your Virtual machines in previous labs.<br>Install the Dovecot application by issuing the following command:<br><source>yum install dovecot</source>#Edit your '''/etc/postfix/main.cf''' file and scroll down to (or search for) '''mailbox_command'''. Add the following line:<br><source>mailbox_command = /usr/libexec/dovecot/dovecot-lda -f "$SENDER" -a "$RECIPIENT"</source>
The diagram above doesn::NOTE: Do <u>'''not'''t even include reading email</u> replace any variables, but those are set automatically by Postfix when it's as simple as it gets (if runs the LDA. If you want to run an email server). You will need to learn to administer basics of all the systems are interested in learning more about the diagram. We won't go in too much depthDovecot application, only the minimum you need. But we will not (for example) go over every detail of Postfix, which on its own has a rather can read about dovecot-lda [httpshttp://enwiki.wikipediadovecot.org/wikiLDA/Postfix_%28software%29#Architecture complexPostfix here] and [httpshttp://wwwwiki.dovecot.org/LDA here].<br><ol><li value="4">Finally, edit the '''/etc/dovecot/conf.credativd/10-mail.deconf''' file and indicate where you want your mail delivered by including the following line:<source>mail_location = maildir:~/Maildir</blogsource></li><li>Restart your postfix-architecture-overview diagram]service.</li><li>While the emails are still stored only on VM3, they will now be easier for other machines/services to access.</li><li>Due to permissions on the directories where mail will now be stored, root will no longer receive mail. Check the logs for an indication as to why.</li></ol>
=== Services involved '''Record steps, commands, and your observations in email delivery ===INVESTIGATION 2 in your OPS335 lab log-book'''
The terms MTA, MDA, ==INVESTIGATION 3: USING THUNDERBIRD (MUA, LDA are not 100% well defined, because few of the related services are simple ) FOR VM2 and do exactly one thing. There is overlap, so if you don't find the acronyms helpful - don't worry about them. But they can help organize your thoughts when trying to keep all this in your head.VM3 MACHINES ==
[http://wiki.dovecot.org/MailServerOverview Here's an overview] of from the Dovecot wiki, it's worth reading.=== Accessing Received Mail Messages on VM3 VIA IMAP ===
In our diagram First, we will set up the IMAP server so we can read email. The current way we have:configured our mail server on our VM3 machine should allow all the email for anyaccount@yoursenecaid.ops should be delivered to our '''vm3''' machine. We will set up Dovecot with IMAP to get easy access to that email.
* A user. That's the person who wants to send an email.* An MUA (email client). This is the application the user uses to send an email. It can be a native application or a web application. We'll set up both types.* Two MTAs. These are the servers responsible for getting your emails to the destination server.** They are similar to routers (whcih route packets) but work on the application layer rather than 'Perform the network layer.** In our example there are only two MTAs - but there can be several.** You connect to your MTA over a secure connection, so your emails canfollowing steps:'t be read by the operators of the network you're connected to.** The rest of the way to the destination MTA the emails travel completely unencrypted, so anyone with access to the routers in between can read all your emails. This is why many organizations will refuse to send you confidential information over email.* The LDA/MDA will receive the email from the MTA, and will store it on disk in some format. MailDir and MBOX are the most popular mailbox formats.* When sending an email you send it to the destination using your MTA, but you also want to save it in your "Sent" folder for yourself. This is accomplished by a separate connection to your IMAP or POP3 server.** This is why it can happen that you sent your email successfully but it never makes it to your "Sent" folder - the second connection to your IMAP server is quite unrelated to the first connection to the SMTP server.* Note that a DNS server is also involved - it's needed to retrieve the address of the email server responsible for email for a particular domain. This is done with the MX records we looked at in the DNS labs.
== Sample client setup ==#The configuration file for the Dovecot service (which is not the same thing as dovecot-lda) is: '''/etc/dovecot/dovecot.conf'''. Modify the '''protocols''' option so that Dovecot will work with IMAP connections, no POP3 or LMTP.# Start the dovecot service, and ensure it will always start automatically when the machine boots.# Use the '''ss''' command to confirm the service is listening, and use '''nc''' on the '''host''' to confirm you can connect to it.# You'll probably fail, so using the information gathered from '''ss''', modify the firewall on vm3 to allow IMAP connections from your local network and try '''nc''' again. Once it works, do not forget to save this change so it will still be there the next time you reboot.#If you can connect - it's now time to do something wrong, that is allow connections to our IMAP server over an unencrypted connection.# Edit the '''/etc/dovecot/conf.d/10-auth.conf''' file and set '''disable_plaintext_auth''' to '''no'''.# Then edit the '''/etc/dovecot/conf.d/10-ssl.conf''' file and set '''ssl''' to '''yes'''.<br><br>'''Note:''' This combination of parameters will allow your username and password to be sent over the internet in plain text, for anyone interested to look at. In a later lab we'll set up secure SMTP and IMAP connections, for now this is all we have time for.<br><br># Restart dovecot so the changes take effect.
Eventually we're going === Connecting to set up all those services, but to begin with we'll set up an email client to connect to a (hopefully) working server - the Seneca email server. This will be a good exercise with an email client.IMAP Servers Using Thunderbird===
Install Thunderbird on your host, and configure it like this, obviously using your own information'''Perform the following steps:'''
[[Image:Seneca-student-thunderbird-#On your '''host''' machine, return to the Mail Account Setup dialog box (eg. near top of lab).# Set up a '''new email-setupaccount'''. You will be using account settings to connect to your '''vm2''' for '''SMTP''' and '''vm3''' for '''IMAP'''.png|600px]]Use <u>no</u> encryption, and use normal password authentication for IMAP. Refer to the diagram below for reference:
Notice that there are unencrypted options available to connect to your SMTP/IMAP servers but those are rarely used these days. The potential for abuse is too great. On a free wifi network the operator would be able to not only read your [[Image:ops335-email - but also get your password, without any password/encryption cracking tools. And even on a private network - it is not uncommon for an employer to sniff all the traffic going over their network (that was found in court to be a legally acceptable practice)step1.png|600px]]
The specific security settings depend <ol><li value="3">Try to connect to your IMAP server with Thunderbird by clicking on how your servers were configured'''Inbox'''. The settings </li><li>If nothing happens, then check the Thunderbird Activity Manager for any errors. If the connection is successful, you should see the seneca servers are [https:'''Trash''' box <u>appear</u> below Inbox.</insideli><li>Use the Thunderbird application to send an email to your myseneca address.senecacollegeIf you've done everything right, it will send the message successfully</li><li>Verify that your message has been sent.caCheck your myseneca email and look at '''/itsvar/serviceslog/maillog''' on vm2 (your emailserver).</email_clientsli></imap.html published here].ol>
After you create your account - you should be able to read your existing email and send new email in === Sending a Mail Message from VM2 (Using Thunderbird.)===
Look through '''Perform the Account Settings and Preferences to get a feel for what settings exist. For examplefollowing steps:* How often will Thunderbird check for new messages?* Will the messages you write be in HTML or plain text?* How do you change your SMTP server settings? Why are they in a different section?'''
If everything #Use the '''ss''' and '''nc''' commands (like you did in lab 4a) to confirm your service is working - thatlistening on the correct ports/interfaces. You will probably have to open the appropriate firewall port on '''vm3''' to allow incoming '''SMTP''' connections.<br><br>'''Note:''s good, now you know what you'll try You should be able to send email to build in any regular user <u>on</u> '''vm3''' using the email labsaddress '''yourusername@yoursenecaid. The goal ops''' using the Thunderbird application on your host machine (which is configured to have use the exact same setup using account on your servers instead of Seneca serversvm2).<br><br>
<ol><li value= MTA for sending "2">Create a new account on your '''vm3''' machine using only your <u>first</u> name. We will use this account as a one-time "test" if the mail message has been received on your VM3 machine (no encryptionfrom your VM2 machine) =.<br><br>'''Note:''' It is <u>'''important'''</u> that you '''<u>don't</u>''' create this same account name on your vm2 machine, since you want to easily identify the difference between the sending and receiving SMTP servers.<br /><br /></li></ol>
We<ol><li value="3">Use the new account in Thunderbird to send an email to '''firstname@yoursenecaid.ops''ll use Postfix as ' and then check the MTA, and wecontents of '''/home/firstname/Maildir/new/'''ll set it up on your '''vm2vm3'''machine. This will There should be a file there with the contents of your email server for your internal network. You</li><li>If there is no file, then check the log file '''/var/log/maillog'''ll be able to send email out of your networksee what went wrong.</li><li>If you can see a file in the '''/home/firstname/Maildir/new/''' directory, and receive then review the procedures on how you got the email from within your network, but not receive from outside your network because:# Outsiders will never find the MX recors for your domain, because there are no .org servers pointing to your DNS server working (since you haven't paid for ithave performed many steps and set up many services).# Even if they did - your local network is using IP addresses on a private subnet, which is not routeable on </li><li>Refer to the internet, so it cannot be reached from diagram at the outsidetop of this lab. Which services have you currently set up? Record your findings in your lab Logbook.</li></ol>
Postfix should be installed by default{{Admon/important |Encountering error messages when sending email|If you cannot properly receive sent e-mail messages, check the '''/var/log/syslog''' file for errors. <br><br> If it isnyou locate an error message in that file such as: '''Fatal: Error reading configuration: Invalid settings...''', then add the following <u>parameter</u> in '''/etc/dovecot/dovecot.conf''':<br />'''postmaster_address <nowiki>=</nowiki> DOMAIN''' (where DOMAIN is actually <u>your</u> domain).<br /><br />After you have saved those changes, then '''restart'''t - go ahead and install ityour dovecot service. Install This problem can also be resolved by properly setting the netstat application (use yum search hostname of your machine to find the package name) and include the telnet commanddomain.}}
Postfix will work with {{Admon/important |Backup your VMs!|You MUST perform a '''full backup''' of ALL of your VMs whenever you complete your '''OPS335 labs''' or when working on your '''OPS335 assignments'''. You should be using the default configuration, so enable it, start itdump or rsync command, and check you should use the Bash shell script that it's running. Also look for it you were adviced to create in the list order to backup all of listening ports:your VMs.}}
<source lang="bash">netstat '''Record steps, commands, and your observations in INVESTIGATION 3 in your OPS335 lab log-atnp</source>book'''
Which one is it? Find the port used by SMTP, and look for connctions with the state LISTEN (i.e. currently listening).== COMPLETING THE LAB ==
== Testing =Online Submission===Follow the connection to Postfix instructions for lab 4b on blackboard.<!--===Andrew's sections===
Connect from You may choose to:* Submit screenshots of your server work on Blackboard, in which case you don't need to come to the lab.* Or come to the lab, show me your server using telnet:work, and talk to me about it. I want to hear what you've learned and answer any questions you have.
<source lang="bash">telnet localhost 25</source>You'll get the same grade regardless of how you choose to submit your work.
Note ::<span style="color:green;font-size:1.5em;">✓</span>Status and configuration of your Postfix service on vm2.::<span style="color:green;font-size:1.5em;">✓</span>Proof that it will tell you once your can connect to that service from the host.::<span style="color:green;font-size:1.5em;">✓</span>Your Thunderbird configuration.::<span style="color:green;font-size:1.5em;">✓</span>The email you sent to your myseneca account.::<span style="color:green;font-size:1.5em;">✓</span>Download and run '''Escape character is wget https://ict.senecacollege.ca/~andrew.smith/ops335/labcheck4b.bash''' on your '^]''c7host', which means your can hold control and press the square bracket key to end the session (and then exit the telnet app)'' machine. ::<span style="color:green;font-size:1.5em;">✓</span>Completed Lab4b log-book notes.-->
If this worked - that means the service is running and listening and responding to connections. Let's see if it works from other machines. Telnet to vm2 from the host (connect to the SMTP port) and see if it works. If your firewall is set up properly - it shouldn't, you'll need to allow incomming connections to TCP port 25.==EXPLORATION QUESTIONS==
Once you open # What is the port in purpose of the firewall - try Thunderbird application?# List the telnet commandsteps to configure your DNS to allow your Thunderbird application to connect to your mail server. You should get a different error this time. This time # What is the purpose of the problem '''Dovecot''' package?# What is that your service isnthe purpose of the '''mydestination'''t listening on parameter contained in the outside interface, it's currently configured to listen only ''/etc/postfix/main.cf''' file?# Why are '''IMAP''' and '''POP''' email servers placed on the loopback separate machines (lovms) interface?# What is the purpose of the '''mail_location''' parameter contained in the '''/etc/dovecot/conf.d/10-mail.conf''' file?# Why is root not able to receive mail with the changed mail location? What could you change to allow mail to be sent to root again?
