Understanding How Email Works
You probably know how to send a message, but not a lot of people know what happens when you do it.
Each message obviously goes through many points on it's way.
I will generalize, because each server is very specific. These points are
1. Your PC. When you use mail client like Outlook or Thunderbird we usually call this computer "mail client" This is where it all begins. Once you press "Send" button, this is where your message is coming from.
2. Mail server you connect to. Any email must always come through one (or usually two or three) SMTP servers. (They are sometimes called mail servers or email servers, whatever you prefer, we will not get stuck on the names, but just so you know).
- Email messages storage. This is where your message will end up after you send it and it is delivered. This is similar to a database of all messages that are waiting for a particular user. In your case, your message will wait for your recipient to read it. Messages never go directly to recipient's computer. Your target recipient will check from time to time if there are messages in his mailbox.
4. Your receiver's workstation. This is where your message is going to end up. When you are sending anything, this is where your message is going to be read.
Let me demonstrate with an example.
Here is Jane, she is sending John a lovely letter about how she liked her date with him, and invites him to another romantic dinner. She is asking him what cuisine he prefers and if he likes French restaurant downtown or that lovely small family restaurant down the street. ..
Ehhh, Yeah, OK. I was talking about SMTP servers.
OK, let's concentrate.
So after Jane wrote this nice message and hits "send" waiting in anticipation, this message is going to her SMTP server. Every user has one, even if you use a free Gmail account or Yahoo or you have Outlook installed, I don't care, you will always, always send your message to SMTP server.
This mail server is a big piece of software... Usually even more than one big piece :) It quickly checks your message headers, looks at the destination (among everything else) and tries to find the server, where John's mailbox is located.
Now, here is that other SMTP server. In some easy case, when both John's and Jane's emails are located on the same domain, like if John's email is john@gmail.com and Jane's email is jane@gmail.com, there is no need to search and of course, there will be no need to contact another SMTP server.
We call it "local delivery". It's similar to sending a letter to a resident of the same building. Just drop it in his mailbox. No need for stamp or postman. See, nothing to it.
Most of the times we will not be that lucky. When John's email is located on a different server, we will need to find where exactly.
We will ask a DNS (Domain Name Server) for the IP address, which is the exact location of John's server.
DNS has a huge database of all network addresses and their IP numbers and it will quickly search through those and give us an answer.
We already know John's email is not on gmail for this example, right.
Let's say his email is: john@yahoo.
SMTP server will take away john@ and will be left with yahoo.
It will then run a special search in DNS (email DNS records have different record type called MX or Mail eXchange). It spits out IP address or addresses of where yahoo.com really is (it can have more than one IP for one name, especially for big providers. Similar to rich boys having many apartments in different cities, but we won't get into that).
Wow. .. Hard part's over... I hope.
Now we are almost at the end phase. All that is left, is to actually talk to the other server and deliver the message to it.
We connect to other mail server, and place Jane's message into the loving care of John's mail server (this is simplified of course, but it is similar to what happens, I just skipped a few steps).
It's not all. We are not over. Now John's server will check if Jane's message is spam, cause. .. well, anything can happen and we will skip this step for now. It will require a separate discussion and it's outside of our scope.
You will need to know it if you plan on sending a lot of messages for your mass mail campaign, otherwise it's not needed.
I will just briefly say this: "Most of mail server's processing power goes to determine if a message is spam". There are dedicated computers running for that on many providers.
Because delivering a message is pretty easy, determining if it's spam or not, is hard.
At this point we are past the spam filter and Jane's message is safely stored in John's mailbox (or should I say in his mail mail store database).
John will now read it at any moment he decides and they can finally agree on the restaurant.
So what is SMTP? Why is it called SMTP? What is behind these letters?
This is just a short version of Simple Mail Transfer Protocol. ..
I don't know what's so simple about it. ..
Perhaps whoever named it, had another, more complex protocol in mind? Well, not really, that's the only one we have.
Brainiacs of the Internet defined it in 1982. Perhaps they consider it simple. ..
But you have to keep in mind, that these guys did not have any instant messenger at that time. They actually used regular mail to deliver messages. I mean manually. I mean on paper. You know, one where it actually involves a postman.
This is a text protocol (well most of Internet protocols are). Back in the day, the brainiacs thought that text is all we will ever need to deliver, so the protocol is all text. So these days, to deliver pictures and files and videos other brainiacs created extensions to that protocol that work around the work around that was created to work around sending text.
Yeeeah, right, OK. Back to the subject.
You will be glad to know, that this protocol is standard for all email servers.
Which means of course, that all the servers on the planet must work this way and they must adhere to the protocol.
Except Microsoft. They have "special" engineers and "special" rules just for Microsoft.
In their infinite wisdom they kinda, sorta support SMTP protocol, but they kinda, sorta don't.
It's not stable enough. I have seen many places where they just did something against the protocol. But since they are Microsoft they are at Ten Tonn guerrilla, sold thy are OK to just ignore it.
But other than that, all others adhere to it and use it.
Here is a high level overview of spam algorithms.
We suspect any message that comes into our mail server and we examine it even before the message comes in we look at the connection it comes from.
Email server examines your IP to see if you are from a "bad neighborhood". There are lots of free and paid services that keep a big list of all the bad IP addresses. SMTP server will check your connection even before you have the chance to start the conversation with it.
It is similar to "we do not open the door to strangers" thing.
After you are past that check, server will verify that the headers you send are correct.
It may check that a domain from which you claim to send your message exists and that it is registered to send email for this IP.
Then it may also check that the return address from your IP corresponds back to the host name you claim to be from.
Naturally, any decent spam check will look at the body of the message and on it's subject. This is what takes the most time. There are special artificial intelligence filters that are trained to recognize spam your messages.
It will also look for some stop words such as FREE, make money fast and so on. The kinds of words and phrases you will often find in a spam message.
About 80%-90% of all of the messages in the world are spam! So much garbage is flying around the glob created by a few people.
Yes, spammers create most of the heavy overhead on the email systems and we, the end users must pay for it. We pay the fees to our ISP.
ISP invest it into heavier infrastructure and lots of filters, just to be able to accept and then immediately throw away 90% of all emails.
by: jas2434ran
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