Re: OT .. Road Warrior communications question

On Jan 27, 11:21 pm, pTooner <geddi...@xxxxxxxxxxxxx> wrote:
Neil N wrote:
On Jan 27, 1:17 pm, Jim Carr <newsgro...@xxxxxxxxxxxxxx> wrote:
Neil N wrote:
Thanks for the thoughts, JIm. Talk of ports is just outside my circle
of current knowledge...
I'll give you a quick lesson. It's not a hard concept. The details may
not be 100% technically accurate, but as far as your practical
understanding, it will be fine. Knowing this info might save you some
aggravation down the road.

The data on the Internet is sent in little packets. Each packet has an
address (your computer, the mail server, a website, etc). Each packet
also includes a port number, which is used to direct the packet to the
proper program at the destination computer.

For example, I'm sure you've been looking at a web page and downloading
e-mail at the same time. A whole bunch of packets of data are hitting
your computer one right after another. The packets addressed to port 80
go to your web browser. The packets addressed to port 110 to go to your
e-mail software. If you're reading newsgroups, port 119 is used.

There are standard ports for a number of applications. One of those
standard ports is 25. It is used for sending e-mail (SMTP).

My ISP, Cox, wants to prevent its customers from spamming or being the
victims of spyware/viruses that spam. So, when it sees packets of data
labeled with port 25, it only passes through those packets addressed to
the Cox e-mail servers. If the packets are addressed anywhere else, they
go into a black hole. This keeps people from hijacking mail servers. It
also prevents legitimate users from accessing any other mail servers.

Likewise, at the mail server receiving the packets, it knows the return
address of the computer sending a packet. The software can tell if the
computer sending the packet belongs to the same network that the mail
server is on. If it's not, the mail server can choose to dump those
packets into a black hole.

So, when you're at a hotel and cannot send e-mail, one of two things
might be happening. First, it might be the hotel's ISP preventing you
from sending data on port 25 to any other mail server except their own,
much like Cox does with me. Another possibility is that your ISP sees
the return address of the data coming from your machine and realizes
your computer is not on their network. The software then just might toss
that data into a black hole.

A third possibility is that the hotel's firewall is blocking any data on
port 25 regardless of the destination. They may not view this as
unreasonable because most e-mail can be accessed via the web.

Why would e-mail work on the web but not from your e-mail software?
Because on the web you are sending the e-mail on port 80, the default
for browsers. The web server receives your e-mail on port 80 when you
hit submit. It then creates the "real" e-mail and sends it to the mail
server on your behalf. Thus YOU are not connecting on port 25, the web
server is.

I hope that makes sense and enables you to ask intelligent questions
next time this happens to you.

Thanks Jim, that does make a lot of sense now to me.  I just verified
the incoming and outgoing ports as set in my office comp's Lookout,
Distress. Maybe next time I'm on the laptop, I might chase down the
issue with the hotel,  just to see if I can.

Question, what email client are you using?
Gerry- Hide quoted text -

- Show quoted text -

The laptop came loaded with Vista ( jury's still out on that) so I've
been using Windows mail.
.

Relevant Pages

  • Re: OT .. Road Warrior communications question
    ... The data on the Internet is sent in little packets. ... The packets addressed to port 80 ... Likewise, at the mail server receiving the packets, it knows the return ... Why would e-mail work on the web but not from your e-mail software? ...
    (alt.guitar.bass)
  • Re: OT .. Road Warrior communications question
    ... The data on the Internet is sent in little packets. ... The packets addressed to port 80 ... Likewise, at the mail server receiving the packets, it knows the return ... Why would e-mail work on the web but not from your e-mail software? ...
    (alt.guitar.bass)
  • Re: OT .. Road Warrior communications question
    ... The data on the Internet is sent in little packets. ... The packets addressed to port 80 ... Likewise, at the mail server receiving the packets, it knows the return ... Why would e-mail work on the web but not from your e-mail software? ...
    (alt.guitar.bass)
  • Re: OT .. Road Warrior communications question
    ... Each packet also includes a port number, which is used to direct the packet to the proper program at the destination computer. ... A whole bunch of packets of data are hitting your computer one right after another. ... The packets addressed to port 110 to go to your e-mail software. ... Likewise, at the mail server receiving the packets, it knows the return address of the computer sending a packet. ...
    (alt.guitar.bass)
  • Re: NAT, Internet access and security
    ... > you just drop all incoming packet that are not specifically allowed in by a ... i think it is a black hole only if it does not respond on any port. ... and that you drop packets instead of reject them. ...
    (Security-Basics)