Thank you very much, Raf. I really appreciate your empathy and all this
help.
I'm reading more and more every day. I really appreciate your support.
The challenge is knowing what matters.
And about your HELO definition, thanks for explaining it. What confuses
me is that clients usually don't have hostnames (like my laptop with its
Thunderbird installation or my smartphone, don't have a hostname or FQDN
to say HELO with), hence making it a requirement is what I don't
understand. It even got me into trouble when requiring it on postfix. I
understand it's valid among public servers, but when we say "client",
that sounds like any client, and not all clients share having a global
hostname/FQDN.
Thanks for explaining EHLO, I think I understand it now.
Cheers,
Sam
On 23/12/2022 5:01 AM, raf wrote:
On Thu, Dec 22, 2022 at 04:47:57AM +0400, Samer Afach <samer.af...@msn.com>
wrote:
If I were you, I'd focus on my lack of understanding of the email protocol.
Now that, is a part that I still cannot fully understand, embarrassingly so.
I still don't know what ehlo means, except that it's the first message. I
don't know why it matters what address we put after it. That does make me
look like an idiot, doesn't it? :-)
There are hundreds of RFCs (at least!) involved in all
the facets of email. Nobody is born having already read
them all. Learning anything takes time. And email is
famously complex. There's an old quote from Sendmail's
documentation that says:
The world is complex, and the mail configuration
reflects that.
But you don't have to read all the RFCs, they are
mostly for implementers. Although I recommend it
whenever you really want to understand the details of
formats and protocols that you are interested in.
It might seem daunting, but it's worth the effort.
Reading a fair amount of Postfix documentation is
needed, though, if using Postfix to handle your email,
and your requirements aren't simple. The
http://www.postfix.org website has links to lots of
documentation. Read what seems relevant to your needs.
And look for tutorials relevant to your needs elsewhere
on the internet as well.
Back to EHLO...
EHLO is the first client message in the SMTP protocol.
Originally, the first message was HELO and it includes
the hostname of the client (so the server knows who is
saying hello). That matters because a lot of mail
servers will check that that hostname is sensible. They
do that because (presumably) a lot of spam comes from
clients that don't provide a sensible hostname.
Ideally, the hostname would be one that matches the
public IP address of the mail server. EHLO is an
extension to the SMTP protocol that causes the server
to send back a list of features that it supports, so
that the client knows what it can do with that server
(e.g., STARTTLS, SMTPUTF8, 8BITMIME, etc.).
cheers,
raf
