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[No audio]

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Sendmail. Sendmail is another one of

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the major service that is used in Linux

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or Unix environment. Sendmail is a

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program that is run in your Linux

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systems to send emails and receive

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emails. But I would say primarily it is

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used to send emails. Because when you

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have a program running in your system or

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or a workflow running in your system,

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and you do wanted to be notified if this

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if the process finished, or if the whole

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workflow finished successfully, you do

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want to get an email at the end. That's

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when you actually have to have some kind

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of mailing program. And the most and

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readily used program that runs in

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Linux is sendmail. So the purpose is,

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again to send and receive emails, the

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files that the configuration files of

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sendmail is /etc/mails/sendmail.mc,

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which is the main file. mc stands for

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mail configuration. And you configure

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everything in this and once you actually

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compile this configuration file, it

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sends all its configuration to /etc/mails/sendmail.cf,

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Many people go straight to sendmail.cf, which is also

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okay, it's fine. It's nothing that

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you're going to break anything. But it

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is a standard and practical

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way that you should always go to sendmail.mc,

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and then compile it, start the

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system, start that sendmail, and it

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automatically push the changes out to

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the configuration file. All the

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configuration file of sendmail is

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located, all the files are located in et

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/etc/mail directory. The service that you

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need to run or start with your system

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start and stop program is systemctl

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restart sendmail. Sendmail is one of

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those programs that does not have d at

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the end. But it does not mean that it's

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not running at all times. It does run in

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the background, it is still a daemon, but

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it's somehow never got a d at the end.

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The command that you will run if you

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want to send email out from your server

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would be mail -s which is an

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option, and then quotes, you'll put a

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subject line followed by the email

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address that you are sending it to. Once

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you send it and hit return on your

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keyboard, it will bring you a kind of

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interactive or like vi kind of mode

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where you will type everything. And then

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once you're done, then you will just

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simply do Ctrl D, and it will get you

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out of that mail program, and it will

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send the email out. So to illustrate

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that more, we will we'll get into our

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Linux machine. And we will look at some

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of the files and commands are related to

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sendmail. So we have our server here,

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we'll log in as ourself, and most likely

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it has already logged in as root. How do

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we verify it, we'll just run whoami,

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which is a command that tells you which

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user is logged in. I'm gonna move the

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window to the side. So we'll see exactly

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what we're doing based on our slide in

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the back. So the first configuration

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file is sendmail. But of course, before

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we get into the files, the first thing

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we need to do, is we need to find out

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whether we have the sendmail program

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installed in our system. And how do we

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need to find that out? There is a command

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that you run rpm -qa, and then

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you grep for sendmail. rpm -qa

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list every single program or repository

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or package that you have installed in

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your system. So I ran it I see it it's

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not there. So the next thing we'll do is

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we will install it to install a package

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you will run yum install sendmail.

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And of course remember that this is

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going to go outside on the internet

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where all the CentOS repositories are

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located and it will get that package

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from there. If you do not have internet

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access on your Linux machine, it's not

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going to work it will fail, it will say, Cannot

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reach the internet or cannot reach the

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repositories mirrors. So once I run yum

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install sendmail, it's telling me that

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it found one package and the size, do you

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want to install it? Yes, of course I do

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want to install it. I'll click Yes. And it

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will start installing it, download,

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install, verify, cleanup, all that stuff is going to go through.

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[No audio]

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Okay, the installation of sendmail is

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completed. Anyway, there is an another

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package that you do need to install,

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which does the configuration of your

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sendmail. And that is sendmail-cf.

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[No audio]

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Click yes to install it.

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[No audio]

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Okay, it is

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complete, it's awesome. So once you have

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the package installed, it means it

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already creates your directories for you

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where they belong, it already creates a

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configuration file for you. So the first

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thing we have to do is go to

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configuration file to define its

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configuration parameters. The

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configuration files, all of them are

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located in /etc/mail, and you will see

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right here, the first third one from the

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top, it says sendmail.mc. This is where

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we will define our mail relay server.

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And what is a mail relay server. Mail

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relay server is a server that is set up

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in a company and environment which will

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accept your emails that are coming from

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any of the server and then deliver. It's

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like a middleman which takes, on the left

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hand it takes your message, on the right

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hand it delivers it. It's a server as

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well. Sometimes it's a Windows Server,

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sometimes it's Linux server depending on

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your environment, but it's a mail relay

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server. Okay, so when we come down to

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this file, anything that starts with

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dnl, it means that it's just a comment,

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you can ignore that, we have to come

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down to a line where it says define some

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SMART_HOST. And the SMART_HOST is our

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SMTP server or relay server where we are

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going to send our emails and it's going

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to accept it. So you just put the host

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name with a fully qualified domain name,

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meaning the host name dot your domain

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name.com, you will add it here. Once that

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is added, and next thing you have to do

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is you have to start the service.

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systemctl restart or start sendmail.

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[No audio]

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Okay, the sendmail service has

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restarted. Let's check the status. It

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says it's up and running. You can also

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check the status of sendmail by running

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the command ps -ef. And then you

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could just simply grep for sendmail. And

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here it will tell you the second one,

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the first one is just telling you the it

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is accepting connections. And this is

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the main process that runs it. You will

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kill it by typing the command kill

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followed by the process ID, 6023. Now you

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could send emails and the command to

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send email is mail -s subject line

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is mail setup. And I want to send it to

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myself. So I'll put my email which is

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imran_ny@hotmail.com. I hit enter. And

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once I hit enter and that's where the

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mail body is. Whatever that you want to

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type the text goes in. hi hellow

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goodbye. And once it's done, all you

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have to do is type Ctrl D, Ctrl D is

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typed, you will get out of your mail

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program, and that's how you send and

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configure your mail. Mail again, once

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again, it's one of the critical services

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that oftentimes you do have to configure

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in your system. So familiarize yourself

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with the mail files, the configuration,

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the how to start and stop this mail

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service, and how to monitor it and how to send mails

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[No audio]