Postfix Problems

[Daniel Hedlund]

> Can anyone point me in the right direction or webpage?  I have search on google
> for this error, but they did not help.
>   
Can you please post the rest of the information about the error (the 
host it was associated with, usually something along the lines of "host 
x.y.z[1.2.3.4] said: ..."?

If the host is not your own computer, the problem may not be directly 
associated with your own server and user authentication, but rather with 
another email server refusing to accept your server's emails.  One 
reason for this could be that the remote server is trying to do a 
reverse DNS lookup of your domain/hostname that represents your server 
and can't resolve it so it's rejecting your emails.  Try the following 
URL of someone who had a similar problem to this (scroll down and look 
at page 2 & 3).  What solved their problem was that they changed 
something in a configuration file from their hostname to their IP 
address, but they do not elaborate too much:
http://www.zimbra.com/forums/showthread.php?t=365

Cheers,

Daniel Hedlund
daniel at digitree.org