Email looping between exchange server and isp

15 pts.
Tags:
Exchange security
Management
Microsoft Exchange
Microsoft Windows
OS
Security
Servers
SQL Server
Hi all we have a problem in that emails that arrive at our exchange 2003 server (server1) that do not have valid recipients in our organisation are being forwarded back to our isp (who incidentially hold our mx records and route email for us). They are then in turn forwarded back to our exchange server thus created this loop. I have an internet connector setup on server1 that use the our isp as a smart host. On the smtp virtual server relaying has been disbaled for all except those in our organisation. Also the option of "foward all mail with unresolved recipients to host" doesnt have an entry specified. Our isp have said they think the problem is at our end but im at a loss to see how? Does nyone have any suggestions? Thanks!

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Normally these mail should be thrown away by the server. Have you configured forwarders or have you got more than 1 exchange server to route between.
Another wild guess would be to check the DNS configuration for your server1 – why does it forward to the ISP. Does it have/get a MX record with the IP address of the ISP?

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  • Serendipity
    In the Exchange Global Settings, Message Delivery properties, Recipient Filtering tab, you can check the check box labeled "Filter recipients who are not in the Directory."
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  • Aalborz43
    Serendipity, IMHO Filtering box should not be checked. According to Microsoft: "Enabling this check box can potentially allow senders of unsolicited commercial e-mail to discover valid e-mail addresses in your Exchange organization, because during the SMTP session, the SMTP virtual server sends different responses for valid and invalid recipients." I think the problem could be on your ISP end, where they have enabled accepting (and forwarding) any emails sent to any address @yourdomain.com. They would need to turn that off. At any rate, since they DO hold MX records AND route your emails, they need to come up with a technically better answer as to why they think the problem is at your end and not theirs.
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  • JimTrouble
    Thanks for all your replies! Our ISP holds our MX records. They provide our spam filtering and virus checking services for our mail as well. They have a filter in place that drops any email that doesnt match a certain criteria and destined for a specific domain (eg. 1stinitial.lastname@abc.com) We have recently disbanded an exchange 5.5 server and now all internet mail is routed thro the new ex 2003 server. The firewall has been adjusted accordingly. The external dns servers on our smtp virtual server are set as our ISP's DNS servers and it is configured to use the dns name of our isp as a smart host. Filter recipients who are not in the Directory" has been checked. Should i disable this? Thanks
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