The magazine of the Melbourne PC User Group How Does E-mail Work? Gordon Woolf

For a while I thought of dropping the word "how" and asking "does e-mail work?" Perhaps we should be surprised that it works as well as it does, but I was prompted to write this when a friend said she had not called on a relative because "he won't even answer my e-mail".

I asked what to me seemed the obvious question: "Are you sure he got your messages?"

We tend to take e-mail for granted, and while it works well perhaps 99.9 per cent of the time, there should never be an assumption that a message gets there, unless you receive a reply.

It worries me that people are increasingly transferring non-urgent but critical mail to the Internet. You can see the problems with real mail: did you in fact post it, did it have the right address or post code or country, did it get put in the right mail box in the right street, did it get taken out of the box by the right person, did it get put on the right desk or in-tray, did it fall into the waste basket, did the right person read it, did they understand it, do they want to do anything as a result?

Be Amazed—But no Maze

If all those things can go wrong with normal mail we should be amazed that things usually arrive, and within a day or two.

We should be even more amazed that e-mail arrives and often on the other side of the world within a minute or two.

However, it is not the somewhat disorganised maze of the early clays. Since the mid 1990s, worldwide, it has been a very organized network owned by big business and some governments such as, in Australia by the Singaporean and (seemingly reluctantly) the Australian government.

Most ISPs, including large ones, use the "backbones" provided by major communications providers the telcos of the world—and generally you will find those data centres where the computers of service providers are installed, are located at the major junctions in telephone cables... just as cities developed at the junctions of trade routes. There are around 8 to 12 tier-one Internet service providers in the world, and they are big business with names you'll know, like AT&T, MCI, NTTNerio, Sprint, QWest and Savvis (which was the US Cable & Wireless). While it is common for them to work on a "peering" basis in that no money changes hands for using each others' networks, disputes are not unknown. One in October this year between two companies that may or may not qualify as being in "tier one", caused problems for millions of direct and e-mail connections when they refused to deal with each other for a few days.

In Australia the backbone providers are Telstra (by far the biggest) and companies such as Optus, Connect.com, UUNET and the revitalised universities network now contracted to Optus. Some of the smaller ISPs have direct peering arrangements with other smaller ISPs to route traffic to each other without going through the major networks.

At a much more local level, Internet service providers can depend on being near the major cable routes. Several years ago a small computer retailer in a Victorian country town wondered why he was continually approached by service providers large and small, wanting to site a computer in his back office. The reason became obvious when one looked out of his back door. At the end of the lane way, perhaps 10 metres away, was the back gate to the main telephone exchange for the region, hidden away behind what used to be a post office.

Where Does It Go?

Who provides your e-mail service? The setup between companies at all levels can be confusing. To take an actual example, you could get an e-mail address from a small Web host based in Australia but find that the company providing the technical services is in California, USA. The computers are actually installed in a data centre (or should that be data centre?) in Michigan with a backup on the US east coast. That data centre is owned by one of the companies that does nothing but provide secure space for racks of computers with connections to the Internet backbone (the tier-one businesses) in multiple ways. They have technical staff who deal with hardware faults and system software, but everything else is controlled by the business in Australia. That is how international we are becoming.

Even if your ISP is a big supplier like Optus (owned by SingTel and therefore ultimately majority owned by the Government of Singapore) you will most likely be connected via Telstra's wires to the local exchange and at some point, either there or at the regional exchange you will start to go on the Optus network and to one of its data centres.

Between major cities you may well be on one or other of the major carrier's cables, but do you remember when a ditch digger cut into the connection at Wangaratta a few years ago? It was found that the two major cables from Melbourne to Sydney were at that point, in the same ditch. There were backups, but not sufficient to cope seamlessly with the two major cables going out at the same time.

When power went out in a large part of the USA due to some faulty planning on dealing with overloads, it was found that two of the seven computers that provided all the Web and e-mail address routing information for the world were not only in the same city, but in the same building. That is no longer true... there are more of them and exactly where they are is no longer common knowledge.

Typically, the data centre my own Web site uses has direct links to three of the tier-one providers and via them has 4500 networks just an extra hop away. That's by no means a great service, but it is affordable.

However, we should not forget that the most common reason why a message does not get to the person for whom it is intended, is that the sender typed the wrong address. It can be as simple as forgetting to press the shift key to get the @ sign (well everything else can be typed without the shift!) Most e-mail programs will alert you if you attempt to send a message without the @, but not all.

What should happen if an address is mistyped, is that your message should bounce back, but it is also possible that your mistyping produced a real address, the recipient doesn't know or understand what you're writing about, regards the message as spam and deletes it.

The Postmaster

One way of checking on addresses is to write to the address which, according to the e-mail standards, should exist for every domain. That is "postmaster@domain.com". Unfortunately some domains are so large that they can't help (put Bigpond and Yahoo in that category), and many smaller ones are set up either without a "postmaster" account or have it diverting automatically to that place called ":null" or ":blackhole" from where nothing ever returns.

The other annoying real life bounces are those that tell you the mailbox is "over quota", meaning it is probably full of spam and that the user has gone on annual holidays without thinking what might happen to e-mail. Some systems usefully tell you that a lk message would be accepted and let the account accept a message that could say something like "Hey, Joe, let me know when you clear your inbox. I want to send you something." Do switch off that nice graphic signature though, or you'll just get another bounce.

And the cause might not be spam. If you send a message with those pictures of the kids attached, and fail to check the size of the files, you could be the cause of others getting an "over quota" message. The most common e-mail inbox size limit is 10 MB, but there are many that have a 2 MB Or less limit. Of course GMail inboxes are huge — you'll never fill those, but, on the other hand it is likely that items sent via GMail will never be deleted ever, even if you send them to the trash.

You may also be sent a bounce which says that mail could not be delivered for a specific period, maybe a few hours or maybe a few days, and that the system will keep trying for a period of maybe three or five days. These do mean what they say, but if a fault has lasted several days already it is likely to indicate a BIG problem, and you'll more than likely get the eventual advice that it has given up.

Too Many Hops

Another likely error message is one telling of too many hops. This is not an indication of someone along the way consuming a strong ale. It means that the message has been transferred from one server to another and another and has done this too many times without reaching its destination.

A common cause is that someone has mail being forwarded to an address that already has mail being forwarded to the other address—in other words, an endless loop. However, there can be cases caused by communication problems, such as if several mail transfer servers in a region go down at the same time, so it is difficult to find a route that works. In most cases the direct connections are between the backbone connections of the sender and recipient, so, while an e-mail message may seem to have many hops, you are likely to find that these have some business connection between the sender and recipient.

For example legitimate hops can be: sender to his or her ISP, to the domain mail exchanger, to the firm owning the computer where that domain is hosted, to the company providing the rack space for that computer, to the backbone provider, and then back up a similar line to the recipient's computer. That may seem a lot, but effectively does not go to any strangers.

Open Relays are generally now forbidden by anyone who wants to stay in the Internet business. If you want to send mail via a domain computer which is not part of your local ISP's setup you will have to prove who you are by providing identification. This is most commonly achieved by forcing you to download mail waiting for you before you are allowed to upload any messages. This is controlled by the "authentication" settings in your e-mail program and can be as simple as telling it to check mail before sending.

BlahBlahBlah

If e-mail is taking a long time to arrive it can be useful to look at the message headers which show just how the message was routed. You will not normally see these but there will be a setting, often under options, which lets you select "all headers". In Outlook Express choose FilelSelect Properties' Details and in recent versions of Eudora there is an option button named "BlahBlahBlah".

You will have to make allowance for time zones but most will show time differences of just a few seconds or at most a few minutes. Where I have found problems they tend to be within an organisation rather than between mail nodes a major service provider taking hours or even days
to transfer a message within its own network, sometimes between cities but sometimes too between mail servers which are possibly on racks within a few feet of each other.

There have been examples in Australia of mail taking days to arrive and the ISPs involved issue apologies and say it will not happen again. However, it does seem that large attachments can be a problem...and this I mentioned in my article on Sending Large Files, PC Update, April 2005. (Basic answer: there are better ways to send large attachments).

Then there can be addresses or ranges of IP addresses that are blocked.

Let's take an example of an actual event. A fellow Web host had trouble contacting one of his clients by e-mail. It bounced with a message that the client's address had been blocked for abuse. But it was not the the address provided by his Web host that had been blocked. The client was still using his local ISP for mail so the IP address that had been blocked was one belonging to the ISP; it had been blocked by its backbone provider.

So a major ISP was blocked on at least some of its addresses by its major supplier. The person sending the message was close enough to phone the would-be recipient but had difficulty persuading him that the problem was not with the sender's tiny business and that it was very likely that the recipient was not receiving other mail. It was big and bigger playing the parts of Dumb and Dumber, but tiny hosting supplier lost a client.

Another ISP also decided for a while to block any e-mail that even mentioned Web addresses they thought of as inappropriate, including mentions of a site that had been mildly critical of the ISP.

Keep It Plain
White lists are intended to ensure that a recipient gets mail they want, but mail rejected by system filters does
12 Months Warranty and 30 days money back Guarantee on not get to a local stage of being seen by the white list filter. Also, some white list entries get a minus score to count against the plus scores of spam: while a score of 2 or 3 can be caused by "faults" such as having a generic address like Hotmail or Yahoo, or using a lot of HTML code, or a lot of images with few words. In one setup I saw, the counteracting score of being on the white list was a measly -0.1 (one tenth of a point).

I know several business owners who filter all messages containing HTML code into a folder which may get a cursory glance before they hit the delete button. HTML code with lots of nice display and with animated icons may be great for messages to your aunt or nephew, but for business messages, to which you want a reply, keep it to plain text. There is a site at www.expita.com/nomime.html which tells how to send plain text in just about every program capable of sending e-mail.

There was a problem with Outlook 2002 (since fixed) by which, when an attempt was made to send messages in plain text, the message was sent with an attachment called winmail.dat that confused more than a few non-Outlook users.

Your e-mail program may also let you ask for notification of receipt of your message, either upon arrival at a possibly correct mailbox, or on being read, or even both. The problem here is that it may produce an annoying dialog box asking whether a response should be sent (I always click `No') or it may put a message in the outbox which confuses senders who know they have not written a message.

Some e-mail setups are not properly planned, certainly not to the extent they should. I saw online advice at a large college which had a frequentlyasked-question "My e-mail messages to the college are bounced back — what can I do?". There were a couple of suggestions and then the comment: If you would like to notify us about your problem, please send an e-mail.


All who use e-mail should have a secondary address. That may be Yahoo or GoogleMail or, if normally using a Web host or domain address, the e-mail address you will have been given by your local ISP.

Check The Sender

There are hopes for the future. For example SPF (Sender Policy Framework). This is an extension to the domain records that tell systems where mail should be coming from. Unfortunately it has not been widely adopted. Every system that receives mail would have to implement some type of SPF look-up mechanism into its mail server, but that hasn't happened.

Microsoft has modified SPF and called it CallerlD for e-mail and then SenderlD Framework but it has not been generally accepted. Yahoo also has a system called DomainKeys that utilizes a public key stored in the DNS records. Again it has little acceptance. Maybe one day...

About the Author
Gordon Woolf, a long time Melb PC member, is a former publisher and an author of several books who recently moved in to Web hosting to cater for small scale publishers.

Reprinted from the December 2005 issue of PC Update, the magazine of Melbourne PC User Group, Australia

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