SMTP best practice (Full Version)

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Label -> SMTP best practice (17.Jun.2008 4:08:42 PM)

I am looking for best practice configuration advice on SBS 2003. We had 4 clients have email bounced from one large email hosting company with a #5.5.0 smtp;550-xx.xxx.xxx.xx (server static ip address) blocked by ldap. returned message.  Each of the four servers are different in configurations for MX records and ISPs. All however had the SMTP routed through DNS.  We fixed each blocked email issue by changing the SMTP from DNS to Smarthost.
 
Have you found Smarthost is better than DNS for routing email?



uemurad -> RE: SMTP best practice (17.Jun.2008 4:17:58 PM)

Smarthost and DNS are not competing features.  What makes one better than the other is the necessity of the environment.

Smarthost sends all outbound mail to a single site which is then responsible for the successful delivery of the message.  Not all environments have this.  Sometimes the smarthost is a gateway product inside your environment, sometimes it's a gateway outside your environment (e.g. your ISP or a mail service).

DNS is used when the Exchange server is responsible for the delivery of the message directly to recipient systems.  It assumes you can establish TCP 25 connections and that DNS can publically query for MX records.

Are you sure that DNS is resolving correctly?  That it is ultimately getting its information from public DNS servers?



Label -> RE: SMTP best practice (17.Jun.2008 4:34:41 PM)

We have not had any trouble with mail from these 4 clients prior to this one host rejecting mail from them one day last week. We tipically configure our servers with DNS routing, but after this we got to wondering if we should consider using smarthosts as our choice. We had other clients similarlly confirgured that could continue to send to addresses at this host.

Just wondering if it others had seen issues with DNS routing and if we should change our setups.

DNS seemed fine. 3 of the four use that same host as an ISP and for DNS. the 4th used another ISP and different DSN servers.

thanks for your help



uemurad -> RE: SMTP best practice (17.Jun.2008 4:54:53 PM)

You might consider flushing the DNS cache on the SBS server, and also performing some manual NSLookup and Telnet tests to see if you can spot any irregularities.



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