Paul M Foster wrote:
> On Thu, Oct 22, 2009 at 06:24:14PM -0700, James Prentice wrote:
> One other note. People look at me like I'm crazy when I mention this,
> but I've seen it quite a bit at various internet mail servers.
> Sometimes, in order to accept email from you, the internet mail server
> must see you *receive* mail within a certain time period prior. That is,
> you have to go fetch your mail at the ISP, which opens a "window" into
> the SMTP server for a limited time. Then you can tender mail to the
> internet mail server. I don't know that your internet mail server
> operates this way, but it's something to consider. I've had to deal with
> this before myself.

This is commonly known as POP lock and is one of the two main ways that
a mail server allows you to relay a message.  If you have authenticated
via POP3 (i.e. checked your mail) in a certain period of time then the
SMTP server will let you send.  The other main one is by authentication
(username/password) with the SMTP server when you attempt to send mail.

> In any case, linuxmanmikec's comment about the internet mail server not
> trusting you on a dynamic IP is spot on. The web of email trust is such
> that internet mail servers only trust other internet mail servers. And
> *your* internet mail server will trust *you*. So to get mail to that
> other internet mail server over there, you'll have to give it to *your*
> internet mail server, which is the only one that internet mail server
> over there will trust. The "bounce" message you got indicates that
> relaying from you is forbidden at the destination mail server.

This is fairly accurate in premise but just to clarify.  Mailservers
don't operate like this by default and there is really no "trust".
There are public blacklists that a mailserver can be configured to use
that tell the mailserver not to accept mail from servers on the
blacklist.  The blacklists may contain servers that allow anyone to
relay email, compromised servers, servers known for spam, ip ranges
known to be held by spammers and *ranges that ISPs designate as dynamic
or used for subscribers (DSL, cable, dial-up customers, etc. because
they shouldn't be relaying email).


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