Jonathan Berry wrote:
On 8/27/05, Craig White <craigwhite@xxxxxxxxxxx> wrote:
On Sat, 2005-08-27 at 00:11 -0500, Jonathan Berry wrote:
Hey everyone,
Okay, a lot of ISPs now block port 25 out to anything other than their
SMTP server. In some situations, it would be nice to circumvent this
to get to another SMTP server if one is not available. So what I had
though is to setup my FC4 linux box to listen for SMTP traffic on a
non-standard port. Actually, I could just have my hardware router
forward whatever port to 25 on the computer, so the non-standard port
part should be easy. It would be nice to have a workable solution
with as little as possible. Does anyone know of some way that I could
maybe take any traffic to my server on my chosen high port and forward
it along to my ISP's SMTP server on port 25? It sounds possible, but
sketchy enough to where it might not be. Any ideas? I figure I could
always just setup my own SMTP server and that should work. But I
would need to make sure I did that right as I do not want to aid in
the spread of spam and/or viruses. Since it would be on a strange
port, it shouldn't be as big a problem, if at all. Any ideas on that
point? So, what do you think of my idea and options? If I were to go
the route of setting up my own SMTP server (perhaps even so far as a
whole email server) any tips as to where to start looking for info on
doing this right?
----
There's often no reason to do what you are speaking of.
You can set Postfix or Sendmail to use your ISP's smtp server as a
'smart host' so outbound email will be delivered. Then other computers
can use the system running Postfix or Sendmail delivering via the smart
host can send mail. The only issue is computers that aren't on your
local lan can't use your mail server to relay mail - which stands to
reason.
If for some reason you really believe you need to do what you are
asking, the following is offered in sendmail.mc (and I presume something
similar is configurable for postfix)
[snip]
dnl DAEMON_OPTIONS(`Port=smtps, Name=TLSMTA, M=s')dnl
and at this point - the ISP's blocking ports 25, 80, 137-139, 445 are
not blocking 587
Craig
Okay, well I guess I should stop trying to be general and explain the
situation. My sister is away at college right now and she has to
connect to the internet through the university's network. Of course,
they block port 25 out to our (home) ISP's SMTP from their network.
The university supplies students with email, but this has to be
accessed via a web interface. They provide IMAP connectivity for
professors, but not students (who knows the reasoning for some
university policies?). So to my knowledge, there is no SMTP server
that she could use to send email with a normal client (she uses
Windows by the way). So, what I want is to setup something to where
should could send email to my Linux server, which would then send it
out to my ISP's SMTP server to go wherever it needs to go. But since
port 25 out is blocked, my server needs to listen on a different port.
I was just going to pick some random, high number like 4539 for
instance. So this is the desired path:
Computer on non-standard port
University LAN
Internet
My Public IP
My Local LAN
Linux Server
ISP's SMTP
Continue just like I was connecting directly to the SMTP server
Does that make sense now why I want this? Is something like this possible?
Yes, and the "standard" approach for this is to provide an SMTP
submission service on your Linux server (port 587). Your sister
authenticates to your server using SMTP AUTH, submits her mail just like
she would with a regular SMTP server and then your server gets on with
the job of delivering it.
If you're using sendmail, search for "MSA" in /etc/mail/sendmail.mc
You'll need to set up SMTP AUTH for yourself, but google is your friend
there.
Paul.
