Question : Error #550 5.7.1 SPF unauthorized mail is prohibited. ##

  Users in my orginization periodically get this message when trying to send emails to certain people outside the orginization. We have an in house Exchange server 2007 and Postini as our spam filtering service. I have reaserched this issue and read some interesting things, but still don't know how to solve this problem. I see that this is an SPF filter problem. Is this on our end or the other companies end? If they add us to the safe senders list will that fix the problem?

Answer : Error #550 5.7.1 SPF unauthorized mail is prohibited. ##

Do you have an SPF record setup? If not, then it is their end, they are being too restrictive.

If you have an SPF record setup for your domain, check you are referencing your sending IP or hostname.

See SPF txt record by typing at command prompt:

nslookup -q=txt yourdomain.com

Shaun