OpenDNS and USF Mail

Recently I started using OpenDNS (a very good service by the way). I have had no problems and the internet is snappier due to less time looking up IP addresses. I have had (and am still having) just one problem: sending mail using my college e-mail address.

I use Mozilla Thunderbird for just about all my e-mail accounts; this includes my college e-mail address. For some strange reason when I attempt to send an e-mail using the school’s SMTP server when I have OpenDNS configured, the server responds back that my IP address is blocked from sending e-mail. The only thing I can think of is that the way Thunderbird sends its EHLO when on OpenDNS causes the server to not allow me to relay through it. This is certainly something wrong with either Thunderbird 1.5 or USF’s mail servers, not OpenDNS. I have currently reverted to sending my college mail through the Tor Anonymous Network until I can figure out how to fix this problem.

Update: I have found the problem; and no, it is not OpenDNS.


  1. That’s really really weird. Will you email contact at opendns dot com with some info about what mail server you are contacting. Are you using SMTP AUTH at all?


  2. David, I am currently investigating what could be the cause before I attempt to contact OpenDNS or the USF Mail administrators (I work for my college’s Academic Computing Department).

  3. I am OpenDNS. Contact me, I think I know what’s happening. When you use a public DNS server they hand back one IP address and when you use their internal DNS server they hand back a different IP address for This is what Paul Vixie calls a “stupid DNS” trick and it’s quite annoying. But that’s just a guess.

    I bet the IP that you are being handed back is for a public mail server that is meant to receive mail only.


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