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Old 08-24-2005, 01:21 AM   #1
mercyop
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Registered: May 2005
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Sendmail and Dynamic IP -> blacklisted


Hi

Have a question related to a bad experience I got some time back.
I'm running a server and have several domain names pointing to it, but I don't have static IP. I update the IP automaticly through nameservers at zoneedit and it works fine.

Sendmail is working fine, I can send, recieve and relay mail. But currently I block the port 25 for following reason.

When I accept incoming connections on port 25 through my firewall my server is somehow blacklisted after some time (happened only once recently, never before) and the consequence is that all traffic to my server is blocked from some locations such as schoolnetworks etc...

The reason given was that mailservers on dynamic ip is a spam server.

How can I avoid this problem with my current setup?
I'm using Debian sarge with sendmail and iptables for filtering ports.
 
Old 08-24-2005, 09:41 AM   #2
GL1800
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Same problem here, AOL, Cingular, Netscape, many others will not allow my sendmail to talk to them. I kept two MUA's set up, one for my domain, and another for my ISP, for a long time. THEN, I discovered "SmartHost" in sendmail. I _think_ this is how it works. He will try to communicate, but, if he doesn't get a receipt, he switches to the ISP server, and sends the mail. I have only a few weeks experience with this, but it certainly seems to be working. You can find setup information all over the web.
 
Old 08-26-2005, 09:34 AM   #3
mercyop
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thanks I will look into smarthost, but I have never had any problems sending mail.

The problem lies in that my dynamic ip adress is banned by some organizations because the server doesn't meet some criteria. Is it simply because dynamic ip and mailserver is a no go, or does the sendmail server have to have some special settings set so that it avoid getting blacklisted as spamserver?

If I use smarthost I don't think that alone will change the fact that my IP gets banned? Having a banned IP for whatever reason can be really frustrating since it usually doesn't just keep you from sending or recieving mail, but all traffic is blocked from certain location (those who use the spamblock organizations lists).

Any more ideas?
 
Old 08-26-2005, 09:48 AM   #4
GL1800
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Yes, you are right, it's the dynamic IP that causes this. Has nothing to do with your email agent, it's just the IP block that you are assigned from. Now, sendmail will NOT get a receipt from these places, rather, a bounce message is returned. He ignores that, and switches to your ISP's mail server, which will NOT be a dynamic addy, and therefore becomes acceptable to those places. The mail goes through n/p. This process is totally transparent to you, and can only be seen by looking in the mail logs. The ISP's addy will NOT be banned, and your IP will not be seen as the sending agent. Now, If someone knows more about this, please chime in, as I am going on little more than observation as to how this works. But, it ENDED the issue for me.

Last edited by GL1800; 08-26-2005 at 09:51 AM.
 
Old 08-26-2005, 10:36 AM   #5
mercyop
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smarthosts sounds like the solution then since I doubt the "spam block organizations" bother to actively scan for servers with dynamic ip
 
Old 08-27-2005, 01:20 AM   #6
mercyop
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Ok I added my ISP as smarthost now and it seems like all post goes through that.

Here's what I added to sendmail.mc:

define(`SMART_HOST',`myispdomain.com')dnl
FEATURE(`authinfo')dnl

And since my ISP demands authentication I added this to the access file, username and the password is in plain text:

AuthInfo:myispdomain.com "smmsp" "I:myispusername" "myisppassword"


My problem now is this (if it is a problem). When hitting mailq I notice that all the messages sent turns up with the message:

(Deferred: Connection timed out with mail.theispdomainaddresscom.)

Last night I was so tired so I didn't bother to test more and today the test mails where actually waiting in my inbox. Looking in the log it seems like all mail was sent through my ISP How is the smarthost function working anyway? Is it queing up all messages for delivery in certain intervals or does it actually try to send the messages instantly? If the last is true my ISP seems to be too slow for the timout.

I tested again today and all mail sent is actually delivered, but not instantly so it seems like there is some interval for smarthost (correct me if I'm wrong).

Last edited by mercyop; 08-27-2005 at 01:22 AM.
 
Old 08-27-2005, 03:03 AM   #7
Pete M
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mercyop

I think your sendmail statement and AuthInfo should be more specific

define(`SMART_HOST',`smtp.myispdomain.com')dnl

AuthInfo:smtp.myispdomain.com "U:smmsp" "I:myispusername" "P:myisppassword"

Not sure if it will help but works for me like this

Pete
 
Old 08-27-2005, 03:17 AM   #8
mercyop
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Quote:
Originally posted by Pete M
mercyop

I think your sendmail statement and AuthInfo should be more specific

define(`SMART_HOST',`smtp.myispdomain.com')dnl

AuthInfo:smtp.myispdomain.com "U:smmsp" "I:myispusername" "P:myisppassword"

Not sure if it will help but works for me like this

Pete
Yes, sorry this is how I have it:

define(`SMART_HOST',`mail.myispdomain.com')dnl
FEATURE(`authinfo')dnl

AuthInfo:myispdomain.com "smmsp" "I:myispusername" "myisppassword"

Do you really think the AuthInfo should have "mail.myispdomain.com" as well instead of "myispdomain.com"? Looking in the log it seems like the request is actually handled by some other subdomain "xxxx.myispdomain.com" and I was afraid that making the auth too specific might make it fail.
 
Old 08-27-2005, 03:34 AM   #9
Pete M
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mercyop

I think it all depends on your ISP mail server, as I said mine works this way but obviously it's a different ISP

For the sake of editing the file and testing might be worth a try

Try to telnet into your ISP mail server see how it answers, here's mine

Code:
root# telnet smtp.blueyonder.co.uk 25
Trying 195.188.53.60...
Connected to smtp.blueyonder.co.uk.
Escape character is '^]'.
220 smtp-out1.blueyonder.co.uk SMTP Service Sat, 27 Aug 200
It always answers as smtp, out1 changes, sometimes it's out6, so I use smtp.blueyonder.co.uk and it works fine

Sorry I can't be more specific


Pete
 
Old 08-27-2005, 03:48 AM   #10
mercyop
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thanks it works as it is now even though there is some minutes delay before deliverance. I will keep this in mind if more problems occurs.
 
  


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