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Zarathustra[H]
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Joined: 30 Dec 2002
Posts: 389
Location: Cambridge, MA, USA
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 Posted: Sun Jun 01, 2003 11:39 pm Post subject: Getting around ISP sendmail (port 25) block... |
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Hi.
As many of you know, a lot of ISP's (Including Verizon which I use) are trying to force their users to use their own SMTP server, which will only accept mail with the ISP email account in the "from" field.
This really pisses me off, and I am trying to find a way to get around it. I'm thinking of trying to either set up sendmail and have it tunnel through an external free proxy server, OR just tunnel through the free proxy server to an external SMTP server.
Problem is, I dont have a clue how to do this...
Anyone know where I can find more information on this subject?
Thanks,
Matt
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xedx
Tux's lil' helper
Joined: 23 May 2003
Posts: 93
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| Posted: Mon Jun 02, 2003 3:19 am Post subject: ? |
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How bout running sendmail on a different port.
Check the docs 
btw use qmail or postfix
you are endangering yourself using sendmail...
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CinqueX
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Joined: 26 Jan 2003
Posts: 58
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| Posted: Mon Jun 02, 2003 3:27 am Post subject: install iptables... |
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#------------Verizon SMTP Server work-around---------------------
$IPTABLES -A INPUT -p tcp --dport 9999 -j ACCEPT
$IPTABLES -t nat -A PREROUTING -i eth0 -p tcp --dport 9999 -j REDIRECT --to-port 25
This iptables rule will listen on port 9999 and redirect your requests to your local mail server. $IPTABLES is usually /sbin/iptables. eth0 is your external interface facing the internet.
Regards,
Cinque |
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joshdr77
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Joined: 03 Jan 2003
Posts: 180
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| Posted: Mon Jun 02, 2003 3:31 am Post subject: |
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hi, i have s imular problem, my ISP blocks traffic on port 80, and my school blocks all traffic on non-standard ports.....is there a way to work around this???
so i can get into my website from school...thanks |
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xedx
Tux's lil' helper
Joined: 23 May 2003
Posts: 93
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| Posted: Mon Jun 02, 2003 3:34 am Post subject: ? |
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| Quote: |
hi, i have s imular problem, my ISP blocks traffic on port 80, and my school blocks all traffic on non-standard ports.....is there a way to work around this???
so i can get into my website from school...thanks
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u can use CinqueX's iptables snip or have ur httpd run on
a different port
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joshdr77
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Joined: 03 Jan 2003
Posts: 180
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| Posted: Mon Jun 02, 2003 3:55 am Post subject: |
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i dont really understand how this all worls.
my ISP blocks port 80
i set my webserver to port 80
and put in that code into my ip tables
and some how it works?
im confused? |
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xedx
Tux's lil' helper
Joined: 23 May 2003
Posts: 93
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| Posted: Mon Jun 02, 2003 3:58 am Post subject: |
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| joshdr77 wrote: | i dont really understand how this all worls.
my ISP blocks port 80
i set my webserver to port 80
and put in that code into my ip tables
and some how it works?
im confused? |
that's portforwarding
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joshdr77
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Joined: 03 Jan 2003
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| Posted: Mon Jun 02, 2003 4:02 am Post subject: |
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yes, i know that, but if all traffic is blocked on port 80, how does my firewall know there is incoming traffic on port 80 and to port forwad all that traffic to another port.... 
ill try to set it up now....but i dont think it work... |
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xedx
Tux's lil' helper
Joined: 23 May 2003
Posts: 93
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| Posted: Mon Jun 02, 2003 4:24 am Post subject: |
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| joshdr77 wrote: | yes, i know that, but if all traffic is blocked on port 80, how does my firewall know there is incoming traffic on port 80 and to port forwad all that traffic to another port....
ill try to set it up now....but i dont think it work... |
ofcourse that wont work if you want it that way.
the iptables rule is only applicable if you dont want to change
your httpd config
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joshdr77
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Joined: 03 Jan 2003
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| Posted: Mon Jun 02, 2003 4:29 am Post subject: |
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LOL, i think we have lost track of my problem, i know i have..
my isp blocks all traffic on port 80 - in going and out going - think - all i know is that when i have a webserver running on that port...i cant get into..
but i run my website on port 8002 joshdr.pointclark.net:8002
at school they block all traffic from non standard ports...i cant get to port 8002.........i cant into into my site....
is there a way around this so i can access my site from home.....ill change ne config which needs to be done thanks |
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joshdr77
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Joined: 03 Jan 2003
Posts: 180
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| Posted: Mon Jun 02, 2003 4:30 am Post subject: |
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LOL, i think we have lost track of my problem, i know i have..
my isp blocks all traffic on port 80 - in going and out going - think - all i know is that when i have a webserver running on that port...i cant get into..
but i run my website on port 8002 joshdr.pointclark.net:8002
at school they block all traffic from non standard ports...i cant get to port 8002.........i cant into into my site....
is there a way around this so i can access my site from home.....ill change ne config which needs to be done thanks |
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Zarathustra[H]
Guru
Joined: 30 Dec 2002
Posts: 389
Location: Cambridge, MA, USA
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| Posted: Mon Jun 02, 2003 4:31 am Post subject: Re: install iptables... |
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| CinqueX wrote: | #------------Verizon SMTP Server work-around---------------------
$IPTABLES -A INPUT -p tcp --dport 9999 -j ACCEPT
$IPTABLES -t nat -A PREROUTING -i eth0 -p tcp --dport 9999 -j REDIRECT --to-port 25
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Thank you...
Which brings back another problem.. I cant get IPTABLES to compile for the life of me. One or more of the modules it uses fails every time I try to compile the kernel with it enabled.
I get an error 2...  I'm going to have to do more research on that...
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xedx
Tux's lil' helper
Joined: 23 May 2003
Posts: 93
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| Posted: Mon Jun 02, 2003 4:55 am Post subject: |
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| joshdr77 wrote: | LOL, i think we have lost track of my problem, i know i have..
my isp blocks all traffic on port 80 - in going and out going - think - all i know is that when i have a webserver running on that port...i cant get into..
but i run my website on port 8002 joshdr.pointclark.net:8002
at school they block all traffic from non standard ports...i cant get to port 8002.........i cant into into my site....
is there a way around this so i can access my site from home.....ill change ne config which needs to be done thanks |
Look for a way to find out all allowed ports...
or try a higher port no.
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xedx
Tux's lil' helper
Joined: 23 May 2003
Posts: 93
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| Posted: Mon Jun 02, 2003 4:57 am Post subject: Re: install iptables... |
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| Zarathustra[H] wrote: | | CinqueX wrote: | #------------Verizon SMTP Server work-around---------------------
$IPTABLES -A INPUT -p tcp --dport 9999 -j ACCEPT
$IPTABLES -t nat -A PREROUTING -i eth0 -p tcp --dport 9999 -j REDIRECT --to-port 25
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Thank you...
Which brings back another problem.. I cant get IPTABLES to compile for the life of me. One or more of the modules it uses fails every time I try to compile the kernel with it enabled.
I get an error 2... I'm going to have to do more research on that... |
what error would that be?
maybe i have already encountered it...
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CinqueX
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Joined: 26 Jan 2003
Posts: 58
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| Posted: Mon Jun 02, 2003 5:21 am Post subject: try this.. |
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I have heard others report similar troubles.. their answer was to re-emerge gentoo-sources. They go to your /usr/src/linux/ dir, back up your .config and do a make mrproper. Copy your .config back to the kernel dir, make your menuconfig and try to compile.
Make sure you do a emerge iptables again.
Good luck. |
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Diezel
l33t
Joined: 04 Feb 2003
Posts: 600
Location: Karjaa, Finland
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| Posted: Mon Jun 02, 2003 6:45 am Post subject: Re: install iptables... |
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| CinqueX wrote: | #------------Verizon SMTP Server work-around---------------------
$IPTABLES -A INPUT -p tcp --dport 9999 -j ACCEPT
$IPTABLES -t nat -A PREROUTING -i eth0 -p tcp --dport 9999 -j REDIRECT --to-port 25
This iptables rule will listen on port 9999 and redirect your requests to your local mail server. $IPTABLES is usually /sbin/iptables. eth0 is your external interface facing the internet.
Regards,
Cinque |
Call me stupid(I am) but I really don't see how this works around the problem. If my ISP blocks port 25, no SMTP server can connect to my SMTP server or am I wrong. Doesn't SMTP's allways try to make the connection through port 25?
Correct me if I'm wron because if I am it's like christmas eve for me. I have Sennmail ready to fire up because I confed it last winter but becaus of the ISP I had to give up.
Cheers
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CinqueX
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Joined: 26 Jan 2003
Posts: 58
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| Posted: Mon Jun 02, 2003 7:29 am Post subject: an explanation.. |
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ISP's typically block SMTP traffic IN to anything but their own SMTP server in an effort to prevent you as a spammer from sending out email to open-relays, and spam friendly mail servers from their IP block.
For this reason, if you do host your own email server, you will be blocked from connecting to them remotely through their packet filtering.
Most mail-admins do not want to have change their default SMTP port from 25, this makes it non-standard, and a pain in the a** for your users to connect to. The solution is to set up a dummy listening port (in this case 9999) that will accept connections and forward them locally on to port 25.
Verizon will likely not be filtering requests to 9999 (its not a popular service port), so requests to 9999 still get through their filters to the email server listening on port 25. Users who don't have this fascist ISP policy can still connect to your server on the standard port.
That was longer than I had intended.. but I hope it helped.
C. |
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fragbert
Tux's lil' helper
Joined: 18 Apr 2003
Posts: 75
Location: Dallas, TX
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| Posted: Mon Jun 02, 2003 7:29 am Post subject: Re: install iptables... |
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| mahellma wrote: | | Call me stupid(I am) but I really don't see how this works around the problem. If my ISP blocks port 25, no SMTP server can connect to my SMTP server or am I wrong. Doesn't SMTP's allways try to make the connection through port 25? |
First of all, no, you are not stupid.  All forwarded SMTP traffic will go to port 25, and there is nothing you can do about it. When a relay server forwards a message, it will check the DNS MX record for the @hostname... portion, and use what it finds there. The MX record cannot specify the port (or even the IP address directly). Basically there is no simple way of hosting your own publicly accessible e-mail server if your ISP is blocking traffic over port 25.
Michael |
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Diezel
l33t
Joined: 04 Feb 2003
Posts: 600
Location: Karjaa, Finland
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| Posted: Mon Jun 02, 2003 7:32 am Post subject: Re: install iptables... |
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| fragbert wrote: | Basically there is no simple way of hosting your own publicly accessible e-mail server if your ISP is blocking traffic over port 25.
Michael |
This is how I reasond it also. Thanks...
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CinqueX
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Joined: 26 Jan 2003
Posts: 58
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| Posted: Mon Jun 02, 2003 8:10 am Post subject: Re: install iptables... |
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| mahellma wrote: | | fragbert wrote: | Basically there is no simple way of hosting your own publicly accessible e-mail server if your ISP is blocking traffic over port 25.
Michael |
This is how I reasond it also. Thanks... |
That premise is flawed. The question is whether your ISP blocks incoming traffic TO port 25 (to prevent you from hosting an email server) OR blocking OUTGOING traffic to foreign SMTP servers.
Either way, MX records have nothing to do with it.
C. |
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Diezel
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Joined: 04 Feb 2003
Posts: 600
Location: Karjaa, Finland
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| Posted: Mon Jun 02, 2003 8:26 am Post subject: |
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The outgoing trafic works fine, but nbothing comes in so that kind of kills the eager to set up an mail server
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joshdr77
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Joined: 03 Jan 2003
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| Posted: Mon Jun 02, 2003 8:38 am Post subject: |
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Hey
to get back to my problem.........Im with OptusNet........in australia......i think that they block incoming traffic to port 80, and not sure abut out going, but it is probably block to...
is there anyway to get a webserver working on port 80 if it is blocked...
im running my server on [url]http://joshdr.pointclark.net:8002/[img] as u can see port 8002......but at school all ports are blocked...
u tried to help me b4, one of you, but u didnt quite understand what im asking.....
i want to be able to run web traffic on port 80......is there any way at all to do this? thanks[/img][/url] |
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Diezel
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Joined: 04 Feb 2003
Posts: 600
Location: Karjaa, Finland
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| Posted: Mon Jun 02, 2003 9:14 am Post subject: |
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EDIT= Sorry DIDN'T read the question properly.
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Last edited by Diezel on Tue Jun 03, 2003 5:39 am; edited 1 time in total |
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Zarathustra[H]
Guru
Joined: 30 Dec 2002
Posts: 389
Location: Cambridge, MA, USA
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| Posted: Mon Jun 02, 2003 2:51 pm Post subject: |
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Hey I'm still working on the IPTABLES problem.. The make mrproper didnt work for me...
Meanwhile..
I have decided, against your warnings (sorry) to use sendmail after all, as my preferred email client (evolution) can interface sendmail directly.
Problem I am having thouhg, is that only root can access sendmail for some silly reason...
| Code: |
matt@localhost matt $ sendmail
bash: sendmail: command not found
matt@localhost matt $ su
Password:
root@localhost matt # sendmail
^C
root@localhost matt #
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Does anyone know why this is, or how to fix it?
Thanks,
Matt
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uzik
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Joined: 17 Apr 2003
Posts: 257
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| Posted: Mon Jun 02, 2003 4:13 pm Post subject: |
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| joshdr77 wrote: | hi, i have s imular problem, my ISP blocks traffic on port 80, and my school blocks all traffic on non-standard ports.....is there a way to work around this???
so i can get into my website from school...thanks |
This can't be right... They're block everything? Why connect you at
all if everything is blocked? Are you sure they just aren't blocking
'proscribed' web sites instead of all web traffic? |
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