Wednesday, November 10, 2004

Smarthosts .... The good, The bad, and The Ugly

Using DNS to route email is a great idea, except perhaps if you're on a dynamic IP Address like myself. Sure it works great for receiving mail, the problem is sending it.

Some domains on the internet consider mail from dynamic IP addresses to be spam, and the message is just rejected. But you're not a spammer (neither is Susan Bradley). What's going on here?

Well, the remote host is doing a reverse lookup on the IP address, which of course, since the SBS server is on a dynamic IP address, won't return the proper domain name. Bam, spam filtered, or so the remote host thinks.

How do you fix this? Smarthost.

Usually ISPs provide an smtp server, that is a Smarthost IP restricted to the IP addresses that they give out. Simply run CEICW and choose "forward all email to the specified host" and put the ISPs smarthost into the box.

Now you're problem is fixed!

Ok, time for some more information, what is a smarthost exactly? A smarthost is an email host that will an email from any email address and forward it to any email address. Sounds like a spam server eh? Yup, that's what it is. ISPs generally use IP restrictions and extensive logging to make sure that you're not spamming from within their network. A report from someone on spam can result in your account being disabled.

So what you don't want to do, is turn your SBS server into a smarthost, but what you might want to do have one SBS server forward mail to another SBS server. How do you do this? On the server you want to be the smarthost, follow these steps:

  1. Open Server Management, expand Advanced Management, {Servername} (Exchange), Servers, {Servername}, Protocols and SMTP>.

  2. Right-click Default SMTP Server and choose properties.

  3. On the Access tab, click the Relay... button.

  4. Click on Add, and add the IP Address of the other SBS server which will use this computer as a smarthost.

**Important: Be extremely careful which IP addresses you add, and do not add any more than neccessary, you wouldn't want your SBS server to be a spam relay server

One last note that when SBS server 1’s IP changes, you’ll have to re-do this sequence.

Enjoy the limited relay


Javier Gomez [SBS MVP] said...

Great blog Sean!

I'm a strong advocate of using Smarthosts in SBS-land. The big ISPs are becoming stricter on what kind of mail they accept and not only they check for PTR records, but for Dynamic IPs blacklists, Open Relay and hopefuly for SPF records soon. Smarthosts is the way to go :-)

FYI-> Here's a link on something I wrote comparing DNS and Smarthosts in SBS: