Open DNS and non-open DNS on same server

Is this possible?

[Lorel]

I'm working on a site that is receiving warnings because the daily SMTP relay has reached it's limit. He doesn't send out that many emails so I suspect an open DNS so was checking his websites (all on the same dedicated server) and some of them show an Open DNS and some only missing stealth name server problems.

How is this possible when they are all on the same "dedicated" server?

[jtara]

Er, you've got your marshmallows mixed up with your peanut butter...

While "Open DNS" is a bad thing, I think you really mean "open SMTP relay".

"Open DNS" really isn't a widely-used term, but I would guess that it would mean that your DNS server does not require authentication for zone transfers. NOT a good thing at all, as it would allow others to possibly alter your DNS records, and at least to view all of your DNS information. (The latter really isn't a huge security threat for most websites - it would allow others to get a list of all of your servers.)

You have another problem with your DNS setup (the "stealth name servers") but again, this has nothing to do with mail. It means that you have name servers listed in your DNS server that you do not have listed at your registrar. Fix it, it can cause problems.

In any case, that couldn't be the cause of your mail problem.

An "open SMTP relay" is an SMTP server that is configured to relay mail received from anybody. Your SMTP server should be configured to relay only mail received from your users, and should require authentication or have some other means (such as checking IP address) to insure that outsiders are denied relays. (Outsiders still have to be able to connect and send mail TO YOU, but they should be allowed to RELAY mail outside of your domain.)

[Lorel]

thanks for this info Jtara, this really helps.