Email Transport Overview

When you send to multiple recipients, it is very beneficial to know how email is transported over the Internet. Therefore, we encourage you to read and understand the information below.

The Internet consists of millions of computers connected together. Some of these computers are devoted to transporting and delivering email. They are communicating with each other with SMTP (Simple Mail Transfer Protocol) and therefore are called SMTP Servers.

SMTP Servers pass email messages to each other until it reaches its destination. When an SMTP server receives a message, it can do one of the three things:

1. Store the message for future retrieval by the recipients.

2. Pass it to another SMTP server, which will be able to deliver the message. This is called relay.

3. Reject the message as undeliverable. If that happens, the SMTP server that was trying to send the message must notify the sender. It usually does this by sending a special email message called bounce.

There exist a special service called DNS (Domain Name Service) which stores so called MX records for each domain. MX record says which SMTP server needs to be used for a particular email address.

So, a typical lifecycle of an email message is as follows:

1. The sender composes a mail message in his favorite mail client such as Outlook Express.

2. Mail client connects to the nearest SMTP server and passes the message to it.

3. The SMTP server looks up MX records and relays the message to another SMTP server which is suitable for the destination email address.

4. Eventually, the message reaches its destination SMTP server and is stored there.

5. The recipient retrieves his mail from the destination SMTP server. Usually this is done with POP3 (Post Office Protocol v3), and therefore the SMTP server which is the last in the chain is often referred to as an incoming (POP3) mail server by the recipient.

Unfortunately, mail system is severely abused by unresponsible commercial advertisers (usually called spammers) who try to send their messages to every email address in the world. Many Internet Service Providers aggressively fight spammers, and since they do not really can tell legitimate bulk mailers from spammers, your mass mailing may be blocked at any stage.

Here is what you should expect:

First of all, you may not be able to even connect to the SMTP server of your choice. For example, Earthlink will not let their users connect to any of SMTP servers except for their own. Worse yet, all your connections may be silently redirected to the SMTP server of your ISP. In this case, all your mail will go through their server and may be controlled, even though you may think you use other SMTP server or send direct.

Then, the very first SMTP server you connect to may reject you based on any of the following reasons:

1. Your Internet connection point is not recognized. For example, if you have two Internet accounts on Earthlink and AOL, then you connect to the Internet using AOL but then connect to the SMTP server belonging to Earthlink. This SMTP server recognizes you as AOL user, not as Earthlink user, and thus rejects all your activity.

2. Your From address does not belong to the ISP domain. For example, you want to send email through your ISP mail server, but spell your return address as aysoft@aysoft.com.

3. You may be required to supply a password.

4. You may be marked as sending message to too many recipients. Usually this limit applies to the number of recipients per single message, which is not a real problem. Some more sophisticated providers may limit the number of messages that you can send per hour, per day, or per month.

5. Some ISP may scan the contents of your message and reject it if they find suspicious words, even though such a behavior is illegal.

Many SMTP servers will do an excessive lookup on all the addresses, which may cause severe delays. Some servers delay communications intentionally to decrease the load.

Once your message comes through the original SMTP, it does not mean that it is going to be delivered, as it needs to come through all filters on the receiving end:

1. Your email may be rejected because it is not personalized.

2. The validity of your return address may be checked.

3. The validity of the original SMTP server may be verified. Some of the receiving servers go very long distance doing this verification. They may connect to the originating SMTP server to find out if the server would relay mail for unauthorized users. If it does, the mail may be blocked.

4. The original SMTP server may be checked against numerous black lists. These black lists normally include addresses of recent spammers and open relays. However, some of the black lists is much more aggressive. For example, DNSBL contains a huge list of IP addresses. They classify all the IP addresses into Internet Service Providers and end users. They look at the end users as potential spammers, and block all the mail from their IPs. Therefore, when you send directly from your computer, part of your email may be blocked.

5. Some recipients may decide not to accept HTML messages, because most of the unsolicited mail is in HTML format.

6. Your message may be checked against the list of forbidden keywords.

Given all these filters, it is getting increasingly difficult to send mass email, and the problem arise now and then with some particular recipients or with whole lists. AY Mail will help you avoid as much of these problems as it can, but you do have to be aware of these numerous problems that may arise.

See also Direct sending versus SMTP