yahoo mail rejected

[jan gestre]

Hi Everyone,

We're using MailScanner for years already, unfortunately there are
some odd things happening from time to time, here is one instance. One
of our client is trying to send an email using yahoo mail
unfortunately our Postfix-MailScanner server rejected the email and
spewed this error message:

From: System Administrator
Sent: Tuesday, June 07, 2011 11:10 AM
To: Jane Doe
Cc: 'MailScanner has detected a possible fraud attempt from
"us.mc768.mail.yahoo.com" claiming to be MailScanner has detected a
possible fraud attempt from "us.mc768.mail.yahoo.com" claiming to be
janedoe at sampledomain.com'
Subject: Undeliverable: Draft NDA


Your message did not reach some or all of the intended recipients.

      Subject:    FW: Draft NDA
      Sent:    6/7/2011 11:10 AM

The following recipient(s) cannot be reached:

      'MailScanner has detected a possible fraud attempt from
"us.mc768.mail.yahoo.com" claiming to be MailScanner has detected a
possible fraud attempt from "us.mc768.mail.yahoo.com" claiming to be
janedoe at sampledomain.com' on 6/7/2011 11:10 AM
            Server error: '450 4.1.2 <MailScanner has detected a
possible fraud attempt from "us.mc768.mail.yahoo.com" claiming to be
MailScanner has detected a possible fraud attempt from
"us.mc768.mail.yahoo.com" claiming to be janedoe at sampledomain.com>:
Recipient
address rejected: Domain not found'

Googling for similar issues led me to none, any ideas why?

Thanks in advance.