[wplug] Blacklisted IP in mail?

[Russ Schneider]

Ok, testing out one machine emailing another, I got the following back 
in an undeliverable mail message:

> <russ at domainname.com>: host mail.domainname.com [xxx.xxx.xxx.xxx] said: 550 5.7.1
>     Email rejected: Blacklisted IP a ddress (in reply to MAIL FROM command)

Here's the details:
1) I mailed this address a few times successfully right before this.

2) The sender was me on one server, and the destination was me on 
another server.  I, as a user of the destination server as well, took no 
action to blacklist an IP.

3) The destination server is one I share with two buddies.  Neither one 
has been online between the time I was able to send email and the time I 
became "blacklisted".

So I'm stumped.

Could this be some automated process in the mail server that blacklists 
an IP if it sends too many emails in a certain amount of time?

If so, where on the destination server does it hold this info so I can 
remove the blacklist (I have root access to that server).

-- 
Russ Schneider (a.k.a. Sugapablo)
http://www.sugapablo.com