Cannot send to comcast.net (Full Version)

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SaumZ -> Cannot send to comcast.net (9.Mar.2006 4:50:13 PM)

Hello,

Our exchange 5.5 server is having a hard time sending to comcast.net

In the outbound queue it is stuck as host unreachable and bounces back within a few minutes.

The nslookup and restest.exe both come back looking good... however... if I telnet comcast.net 25 I do not get a responce.  When I telnet on port 25 using their MX entry ip's, I get an immediate response.

It sounds like a DNS issue, but I am not sure where to start.

EDIT: I just set the dns IP to my ISP's DNS instead of my internal one.  I tried the telnet comcast.net 25 and it came up with a connect failed, but the telnet with the ip address connected fine right away again.  Could it be my isp's fault?

Thanks in advance,
Jayson



bgcarter -> RE: Cannot send to comcast.net (9.Mar.2006 9:31:49 PM)

Hey.  I had the same problem with hotmail.com and msn.com. 

I contacted hotmail/msn (suprizingly, very helpful guys there!) and we tried all of the things you have done.  And they confirmed that there was no blocking on their end.

They use 8 different IP addresses for load balancing with only 6 of them in use at any time (so there are always 2 "dead" ip addresses).  I even tried bypassing the whole name resolution thing by putting a current "hot" IP (supplied by the MSN guys) into my HOSTS file.  No joy.

What finally worked is that I changed the PRIMARY DNS server on the 5.5 box and pointed it to one of the SpeakEasy name servers. (66.93.87.2 in this case)  NOTE: SpeakEasy is NOT my provider.  XO.com is (and they suck, by they way).

...and ZINGO out went my OUT queue!   

I would try using a couple of different KNOWN GOOD DNS SERVERS and see how it goes.

-bgc



SaumZ -> RE: Cannot send to comcast.net (9.Mar.2006 10:09:33 PM)

I've tried a few different name servers, no dice.

I can try a few more...  do the root servers allow direct connection? lol

EDIT: I just tried putting comcast's own NS as my primary dns server, still no go.

I'm not sure if that is the issue 100% now.  Could there be something corrupt in exchange so that it doesn't like comcast? 



bgcarter -> RE: Cannot send to comcast.net (9.Mar.2006 11:02:33 PM)

Check your Delivery  Restrictions.  If there is no problem there, check the CONNECTIONS tab and the Accept Connections section. 

If all is good there this is what I did.

Using some other SMTP server (there are freeware ones out there) installed on another machine try sending a message.  Make sure that the new SMTP server is on the same subnet and on the same side of the NAT as your 5.5 server.   Make sure the appropriate ports on your WAN  router are configured.   If the message gets through, you definately have a problem with the  Exchange box.  If it doesn't get through then your problem is either name resoltion or network related. (PS:  if you don't get a resoponse, be sure to try other addresses NOT on comcast.net to confirm you have your SMTP set up right)

One other thing.  Do a ping sweep of the subnet your ISP has you on.  Likely you will find one or two other entities.  Run a WHOIS on them and give them a call.  Ask what kind of email server they are running (if at all) and ask if they are having the same problems you are.   If they are, you have a very strong case when you call your provider.  If they aren't well, at least you got to know your IP neighbors---always good info.

Good luck.

bgc



Xguru -> RE: Cannot send to comcast.net (10.Mar.2006 12:13:54 AM)

You said when you telnet it just drops the connection?

Are you sure you are not blacklisted in comcast?

Try a telnet from a system outside your network and replace the mailfrom part in the below example to yorename@yourdomain.com

220 rwcrmxc24.comcast.net - Maillennium ESMTP/MULTIBOX rwcrmxc24 #338
ehlo ramee.com
250-rwcrmxc24.comcast.net
250-7BIT
250-8BITMIME
250-DSN
250-EXPN
250-HELP
250-NOOP
250-PIPELINING
250-SIZE 15728640
250-VERS V05.00c++
250 XMVP 2
mail from: saasjask@ramee.com
521-EHLO/HELO from sender 202.81.131.64 does not map to ramee.com in DNS
521-sending machine name must be provided as a fully
521-qualified domain via EHLO/HELO command.
521-see section 4.1.1.1 and 4.1.4 of RFC 2821
521 521: Comcast requires that all mail servers must have a PTR record with a va
lid Reverse DNS entry. Currently your mailserver does not fill that requirement.
For more information, refer to: http://www.comcast.net/help/faq/index.jsp?faq=E
mail118405
 
If you get prompt like what you have below possibly you may be blacklisted.
 
XGURU
 



SaumZ -> RE: Cannot send to comcast.net (10.Mar.2006 12:23:51 AM)

I have verified with comcast that my IP is not on their blacklist.



Xguru -> RE: Cannot send to comcast.net (10.Mar.2006 12:31:48 AM)

Can you try and install ethereal and capture the traffic? It can provide lot of information.

XGURU



SaumZ -> RE: Cannot send to comcast.net (10.Mar.2006 3:59:00 PM)

Wow, the ethereal capture worked wonders.

It says that we are blacklisted on by comcast, even though comcast says we are not, and the telnet window says we are not.

Real interesting.

I will be contacting comcast.

Thanks!1



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