MAPS List
I use these two for maps
sbl.spamhaus.org;bl.spamcop.net
just like that, cut and paste it into the maps section in plesk.
As far as the undeliverables, I have tracked that down to this:
The plesk scheduler service wants to do a few things on a fresh install, what I have seen is that it can not verify the sending domain name such as admin@localhost or scheduler@yourcomputersname
the "yourcomputername" is that, the name your computer has, it seems it wants it to be a domain or something, .com and needs to resolve before it sends its email out. I have ahd major trouble with the scheuler service in plesk, and have yet to see it work, namley because of this problem. Funny thing is, the computer name can not have any charecters other than alph/numeric meaning no . i have yet to figure that one out, although it may be becasue I am using 2k3 web edition and not the full blown 2k3..not sure but I am not happy bout plesk, lack of support, limited options for web serving and crappy software
The maps will help to fight spam incomming to the domains, also check your php.ini file C:\winnt\ for any reference to the failed emails.