In this video, Chaim Krause reviews the path that an email takes as it travels from sender to receiver. The names of the parts involved are covered along with the linkages.
- [Instructor] Before we go into building our email server, let's review what it's like to follow an email through the system and the various parts that are involved so that when we start building it we know where it fits in the big picture. So let's look at what we've got here. The first thing is Email Creation. You're going to have a user who's going to interact with an MUA or a mail user agent, which is just an Email Client, something like Thunderbird.
And it's going to create emails and store emails on the file system. But eventually, when user wants to send one off it's going to be sent off to the next location. Transporting the email from the mail user agent to the mail transport agent is where the SMTP protocol comes into play. Now depending on how you have things set up, there may be a message submission agent included in the process and that server is going to temporarily store that email in its local file system.
But that's not the destination we want to get to. So the next step on the path is sending it to another MTA. This may be called the Mail Exchanger because it's what is listed in the MX record, or mail exchanger record, in the DNS. And it's going to accept the email. It may also have an MSA. And it's going to receive the email and put it in its local file system so it can process it further. There could be any number of servers in between doing the same thing.
But eventually it's going to get to the final destination, the final mail server. And the next step in the process is going to be a mail delivery agent or your local delivery agent delivering that to the local file system of whatever computer is storing the files. It could be database storing the email. It could be the actual file system of a network-attached storage. But somewhere the mail is going to be delivered to a spool.
Eventually it'll be picked up by the recipient of the email. Now, the next portion here can go one of two ways. Mail Retrieval can be done if you have a mail retrieval agent that processes email before you actually look at it. So it may take it and then use something like Sieve to take the email and put it in the proper folders, annotate it specific ways, and then put it in the file system to be picked up by its recipient.
Another path that it can take is it can be stored on a POP3 or IMAP daemon so that the user can access it, not through a local file system, but over a network and retrieve it from a server. In order to do that, we're going to need another MUA and that's also going to be an email client like Thunderbird. And it'll use POP3 and IMAP protocols to retrieve the email from the server. Eventually it gets to a user where it's stored in that local file system at the ending point of this traversal.
So as we go forward, we'll be building the various parts that go into this process. And when we're all done, we'll be able to deliver and receive email at our email server.
- Reviewing the components of email delivery
- Sending mail with Postfix internally and externally
- Configuring TLS, SASL, and an email client
- Installing database tools
- Creating virtual domains, users, and aliases
- Exploring greylisting with Postgrey
- Installing and configuring spam tools
- Reviewing DNS-based protection against spammers