ARGH! Just when I thought I had everything figured out:

ERROR: One or more of your mailservers does not accept mail to postmaster@mysite.org. Mailservers are required (RFC822 6.3, RFC1123 5.2.7, and RFC2821 4.5.1) to accept mail to postmaster.

mail.republicanblend.org's postmaster response:
>>> RCPT TO:<postmaster@mysite.org>
<<< 550 Requested action not taken: mailbox unavailable or not local

So, I now get this for several new domains that I created through Plesk. I have some other domains, which are in the same TLD as my nameservers (.biz) and they do not show this problem.

What gives?

You don't have postmaster accounts for those domains. That's a problem that needs to be fixed not in DNS but in your mail server.

So, I guess that makes it a Plesk problem....Wonder why it created them just fine for the other domains...

Ah well, manual will do I guess.

Thanks.