Aug 172019
 

There is a quite amusing social media feed shaming the poor behaviour of airline passengers which is fair enough – some of the behaviour is quite nasty and shaming it is quite reasonable.

But they also seem to have a foot phobia – naked feet are themselves considered sufficient to be worthy of public shaming. Why?

Now I am not talking about sticking your naked feet in someone’s ear, or anywhere else that closer to someone’s nose than necessary. But on the floor? Why not?

Well there are those who are horrified by the sight of naked feet, and without a good reason there is no harm in not horrifying them.

But there are sometimes good reasons – I have psoriasis and wearing socks and shoes in a warm environment results in sweaty feet. Which in turn results in socks feeling like a cheese grater on my suppurating sores on my feet.

So screw your anti-foot fetish; I’m getting my feet naked whenever I feel the need for it.

The Window

Jul 272019
 

Back when the Brexit referendum result was announced, I (as a remainer) was reasonably content that we should have Brexit – and then start campaigning to rejoin the EU. But things have changed.

What has not changed (but is still worth reminding ourselves) is that the margin of victory was very narrow – the Leavers like to claim there is a clear mandate for leaving the EU. A mandate yes, but any referendum that is won by such a narrow margin is not exactly a “clear mandate”.

And it has become clear that the referendum campaigns were conducted in a way that was probably in violation of UK law – questionable funding sources, connections to some very dubious US ‘politicians’ and of course the Russian connection.

Various credible sources have indicated that Russian social media trollbots were very active during the lead up to the referendum.

Does this invalidate the referendum result? It would not be totally unreasonable to argue that it does – whilst disregarding the referendum could well be regarded as undemocratic, the level of interference in the referendum is also undemocratic.

But rather than concentrating on that, let us take a look at “no deal”. The referendum was not asking whether we should crash out of the EU with no deal; the implication was always that there would be some sort of deal to our benefit (although why the EU should agree to a deal favourable to the UK was always a bit questionable).

So all those who voted for Brexit were not necessarily voting for “Brexit under all circumstances”; they were voting for a Brexit with a beneficial deal. In these circumstances, it is more democratic to cancel Article 50 if no deal is possible – only extremists want a “no deal” Brexit.

Because that was the choice in the referendum – remain, or to leave with a decent deal – because all the leave campaigners were saying we would get a good deal.

The Paths Meet

Jul 172019
 

Trump’s twitch. No not that one, the tweet about certain congresspeople “going home” (despite the fact that of the four women targeted, three were born in the USA).

Quite rightly it has been labelled as “racist” but without meaning to minimise that criticism, that is a personal insult to the four women (and we can get outraged on their behalf). But something that has been less pronounced: it’s also an insult to every single voter who elected those four women.

Trump was criticising those four women because they are criticising US government policy; as duly elected representatives and part of the US government, they are doing what they were elected to do. Criticising those women for doing their job is essentially saying they are not entitled to do their job and in turn those who voted for them are not entitled to their say.

And this attack on democracy is as important to highlight as the racism.

Jul 132019
 

This question popped on Twitter just now; I’m not sure the question was a serious one, but as it happens I can answer the question as if it were serious. I’ve been running relatively small mail servers for nearly 30 years, so do know a litle bit about it.

This of course does not cover lots of “bolt ons” to email such as SPF, DKIM, DMARC, and that’s just the simple stuff.

To keep things relatively sane, I’m going to gloss over an awful lot of details – for example, there are all sorts of ways of composing and sending emails, but I will assume you’re using some sort of web interface such as Google Mail.

So you compose an email with an interesting picture or two, and click “Send”.

Hang on a bit! You also did some technical stuff when you entered an email address into the “To” field (if you just enter someone’s name, something somewhere is changing that to an email address) and possibly something summarising the email (or trying to get attention) into the “Subject” field.

Headers

Those two headers you have filled in – ‘To’ and ‘Subject’ – are just two of a whole collection of headers that are usually invisible. They are invisible because your mail client is hiding them from you; for good reasons as they’re almost always an unnecessary distraction.

But when you have to diagnose an email problem, seeing the full set of raw headers is kind of essential even if it is dead simple (for the relatively technically sophisticated) to forge headers.

For example, if you set up a dedicated mail client rather than use your mail provider’s web-based mail client, you will have to fill out your own email address (to go into the “From” field). You can fill anything you like into that field although you are unlikely to get a reply

Email Addresses

If you fiddle with your mail client enough, you will realise that the “To” field can be changed to a “Cc” field or a “BCc” field. All three take email addresses, and can be used to send an email to someone but they operate in very slightly different ways.

The “To” header is for the main audience of a message.

The “Cc” header is for an audience who should also see the message, but perhaps don’t need to take any action based on the email.

The “Bcc” header is a bit special because it isn’t added to the raw mail message as a header, but is instead used to compose the envelope listing who should receive the email. If you need (or should) keep the list of people receiving an email secret, or just want to avoid an inconveniently long header for people to read then use the “Bcc” header.

Although your mail client may hide the details, email addresses look like :-

  1. some-name@example.com (a “pure” email address)
  2. “Some Name <some-name@example.com” (as normally formatted)

The Message Submission Server

So you click on “send”. What happens then?

The first thing that happens is that your mail client converts your email (attachments, rich formatting, etc.) into plain text which is why a file attachment just under your ISP’s limit on mail sizes can exceed that maximum.

To the top of that plain text version of your message, your mail client attaches some headers (again in plain text). In addition your mail client will prepare an “invisible” envelope independent of the headers – it contains just the address(es) you want to send to, and your own address.

Finally the mail client is ready to talk to the “mail submission server”. It will login (usually) with your credentials, and sends the message to the server using the “Simple Mail Transport Protocol” (SMTP).

The mail server adds your message to a queue and before it says to your mail client “Okay, I have it”, it will make sure that the message is safe on disk. Mail servers go to a lot of effort to make sure your messages don’t get “dropped on the floor” even when the operating system they are running on crashes.

The Journey

After you have submitted a mail message to the message submission server, the message is held in a queue. This is significant because email is a store and forward messaging solution, so every server your message journeys through will make sure it is stored on disk before saying to the server sending the message “Yep. Got it.”.

In theory this should mean that messages never get lost “in the system” (although practice is often different to theory). The store and forward style of architecture suits the era that email is from – back in the 1970s when email could (and did) traverse many different kinds of network rather than “the Internet” that we have today.

What does that mean today? Amongst other things, it means that whilst you may think that your message only visits two mail servers – the one belonging to your ISP and the one belonging to the recipient’s ISP – and that is certainly a valid architecture for very small organisations.

But it does not work so well for larger organisations that may handle millions, or hundreds of millions of message a day. Summing up a large architecture without actually seeing an architecture diagram for every single ISP and large organisation on the Internet is going to be a bit hit and miss, but I’ll give it a go.

Your message submission server will probably simply hand your message off to a server responsible for sending email messages across the Internet. If it cannot send to the recipient’s receiving mail server on the first run through the queue, it may well just hand the message off to a “slow message server” (processing large queues is a bit of a drag).

In either case, the recipient’s server will accept the message and then hand it over to a “mailbox server” that the recipient will connect to.

And the journey is over. At every stage, reliability is favoured over speed.

How do servers send your message to each other? Using that SMTP standard I mentioned earlier.

Speed

The speed of email is a good topic to cover here. Speed is not what email is about in the same way that the postal service for physical letters is not about speed. It’s about reliability

Your messages may be readable by the recipient within 5 minutes 99 times out of 100, but that 1 time may take a day or two. That’s just the way that email works – if you want instant messaging, use an instant messaging client.

Security

At no point have I mentioned encryption, and that is intentional. At no point is encryption required; email was designed in an era when computers were far slower and encryption was expensive (even though it was far weaker).

At every point, servers are trusting that the senders are not lying and the original sender is trusting that nobody is snooping on their emails.

To correct that there are a whole bunch of optional add-ons to the email standard to deal with that. But that is a story for another day.

End of the Pier
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