Email Settings - and why sometimes sending doesn't work

By Lindsay,
Simple POP/SMTP email is great when you are at home or at work, and your home/work computer doesn't move around.  If you are a Xtra customer, your email settings will have you using Xtra settings.  i.e  pop3.xtra.co.nz, smtp.xtra.co.nz can be found in the accounts property box of your email account.
Email was designed (remeber in the 1970's) to allow for a concept called relaying.  Email was after all built around the dual concept of:
1.  Email can be passed to someone else to pass on if I can't get through (relaying), and
2.  Email isn't critical because, well, if it was critical you would phone or fax....

Let's not deal here with concept 2.  We now use hosted exchange email delivered to multiple devices in real time to solve that little issue.

But concept 1 - relaying - whilst a good design concept, was quickly seized on by spammers as a means of sending email to people, pretending to be someone else.  So the ability for email to be relayed has been turned off.  Internet service providers still needed to send email so the basic concept is that if you are using an ISP for broadband, then that ISP will accept your email for sending because it knows who you are. 

So in the real world, say, you use Xtra, and have an address@xtra.co.nz.  At home you use Xtra as your ISP, and you want to send an email.  Xtra will accept the request because you are using their broadband circuit, and so it know you are a valid Xtra customer.  You then take your computer to someone elses place.  They use TelstraClear to provide broadband.  You go to send an email (via Xtra).  It is stopped by TelstraClear because they don't know if you are a real Xtra customer, or a spammer.

There are slight variences to this scenario, and in fact Xtra use other techniques to allow emails to be sent/received no matter which ISP is used. (Good on you Xtra, I wish TelstraClear would adopt the same trivial to set up technique!).  But protecting us from spammers is the reason why you can sometimes send emails from location A, and not from location B, if you use an @Xtra or @clear.net.nz or @eol.co.nz email address.