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Problems caused by our ISP being on a DNS blacklist

Posted on 2006-11-28
Medium Priority
Last Modified: 2010-05-18
We run Exchange 2003 in our organisation. Our ISP is Demon.

Today I have been receiving emails bounced back to me with text similar to the following:

554 Fasthosts is not accepting mail from [ Client host ; ] at this time.  Please contact quoting this full error message.;

If i do a lookup on it comes back as (ie my ISP's mail server)

I have contacted Demon to get them to try and remove the mail server from the blacklist but in practice I know this can take several days.

I just wondered if anybody else has had the same problem with their ISP getting blacklisted and whether there is anyway round it. For example, can my exchange server act as an SMTP server in it's own right or do i need to send through Demon? In my ESM I have a connector called ADSL which forwards all mail to Do i need to use this?

Question by:metamatic
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LVL 23

Assisted Solution

by:Stacy Spear
Stacy Spear earned 300 total points
ID: 18029975
I would send from your Exchange server. You may have to configure it connect via 587 (secure smtp port) in order to bypass port 25 filters most ISPs put in place.

You can do this by the following copied from

How to Change the Outbound TCP Port
NOTE: Every remote SMTP server that you want to communicate with must be configured to accept connections on the specified port. In most cases, you do not want to change the default port setting.

To change the outbound TCP port, follow these steps:
1.      Start the Exchange System Manager.
2.      Locate and click Servername, click Protocols, and then click SMTP.
3.      Right-click the Default SMTP Virtual Server object, and then click Properties.
4.      Click the Delivery tab, and click the Outbound connections button. Set the TCP port to 26 (or whatever value you require).
5.      Quit the Exchange System Manager for the changes to take place.
All outbound SMTP traffic is now sent to port 26 on other servers.

NOTE: For these steps, the Display routing groups check box is enabled on the Exchange Organization Name properties in a mixed mode site.
LVL 23

Expert Comment

by:Stacy Spear
ID: 18029988
Note that a small percentage of servers are misconfigured (well a lot are misconfigured) and won't accept connections on 587.
LVL 12

Assisted Solution

Donnie4572 earned 300 total points
ID: 18030752
You should remove the smarthost/connector and create a new connector and allow exchange to send mail to the internet using port 25.
You should plan for this to prevent extended interuption in your mail flow.
For you incoming mail, is it delivered to the smarthost or directly to your exchange server?
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LVL 104

Accepted Solution

Sembee earned 1400 total points
ID: 18031322
I would dump Demon Internet.

This isn't the first time their mail server has got listed and if they even bother to lift a finger I will be surprised. If you haven't already gathered, they have this attitude to the internet that they know best - just because they were the first dialup ISP in the UK to charge the flat rate (but the last to offer an 0808 dial up number).

Change the SMTP Connector to use DNS and see how much of your email gets delivered. If you find that you have problems with some domains then look around the internet and pay for a relay server from someone else.

In short - if you value your email either inbound or outbound then you do not use Demon's email servers. I have seen emails go in to their cluster and not come out again for six weeks.


Author Comment

ID: 18067539
Thanks for the replies. Demon responded to my email saying they had sorted out the issue which had caused them to be blacklisted but that SORBS wouldn't take them off the blacklist because they weren't prepared to meet SORBS demands to implement real time outbound spam filtering or make a donation to charity.

Anyway, in the last few days I've not had any emails blocked so I assume both parties have come to some sort of arrangement.

Simon - I have no love for Demon and intend to move away from them at some point. I hear good things about Zen Internet. Do you have any opinons on them or can you recommend any other UK ISP?

Also, can any of you recommend a knowledge base article or guide to moving over from a Smathost to sending direct from Exchange?

LVL 104

Expert Comment

ID: 18068234
My primary choice for ISP in the UK is Pipex. The second is Eclipse.
I would suggest that you spend some time on (previously known as as that will help you make the decision.
I haven't use Zen personally so cannot comment on their performance. What you need is an ISP that will give you at least one (preferably a few) static IP addresses, will set a reverse DNS and doesn't block port 25.

To change the delivery from smart host to direct, simply adjust the SMTP Connector in ESM. It is a radio button to switch between the two.


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