On Jul 22, 2007, at 7:17 AM, Yersinia wrote:
I didn't understand the reason WHY, i.e., "ISPs don't permit
relaying,"
Relaying is when they accept an email for a mail server that isn't
their own. In other words, my mail server will always accept mail
addressed to anything on the mythtech.net domain because those are
local addresses. But if you tried to send email to someone with a
yahoo.com address and send it using my mail server, it will refuse
the email because that would be relaying, you would be asking it to
accept the mail, and then pass it on to yahoo.
Mail server refuse this by default because that is how spammers get
their mail out.
Mail server WILL relay when certain conditions are met. If they
didn't, you would never be able to send email to other people. Those
conditions vary depending on the mail server, but generally they
revolve around some form of authentication. Some ISPs use what is
known as IP Authentication. They check the IP address of your machine
when you try to connect, and if it from a list of known safe
addresses (ie: addresses of their customers), then they accept the
email. This is common with cable providers and used to be common with
dial-up providers (may still be with dialup).
Other forms are POP Authentication, which is when you check your
email, the mail server records your IP address, and grants that
address permission (via IP authentication) for a limited period of
time. Usually 30 seconds to 5 minutes. This was common when
authentication was first starting to be used because it enabled any
email client to support authentication. It has started to fade away
as most mail clients have been upgraded to support SMTP
Authentication which is more secure.
SMTP Authentication is probably the most common form these days. With
SMTP Authentication, you actually log into the mail server before
attempting to send your email. You send it your username and password
when you start the connection, and if they match the mail server's
records, it allows the connection. If not, it refuses it. This is
method is more secure than IP Authentication (which can't take into
account compromised computers or networks), and POP Authentication
(which can't determine if the IP address it approved is actually
still in use by the person that had it approved, although by keeping
the allowed time window short, the danger of POP Authentication being
abused is exceptionally minimal).
The downside to SMTP Authentication is, your mail client must support
it. Most modern mail clients do, but it still causes some headaches
for people using old software for whatever reason (like you Emailer
users, as well as there are tons of automated system alert systems
that don't support SMTP Authentication for sending their alerts).
but I expected to have to be able to connect to my own ISP in order
to do
email while I'm away from home this week
You should never need to connect directly to your ISP in order to
collect your email. Sending can be a different story, as that will
depend entirely on how your ISP has their mail server security set
up. Last I knew Cablevision around here does not accept email relayed
thru their server from off their network. No ifs, ands or buts. So if
you were a Cablevision customer, had a laptop, and were on the road
some where, you would be SOL on sending email unless you had an
alternate mail server you could use. (when on the Cablevision
network, they use IP Authentication which is nice as you don't have
to worry about any kind of authentication settings). But I think
Cablevision is in the minority in their practice of totally refusing
mail relays from off network. Almost all other ISPs allow some form
of off network authentication, such as the above mentioned POP or
SMTP Authentication.
So there is a really good chance you would be able to send your email
from your BF's ISP as long as you could authenticate via whatever
method your ISP requires.
-chris
<www.mythtech.net>
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