Confuddled over postini

[#1]

Early today I received emails that appeared to have come through the postini mills. All the emails were genuine. Here is an example extract.
Received: from exprod5mx212.postini.com ([64.18.0.71] helo=psmtp.com)
  by pih-sunmxcore15.plus.net with smtp (PlusNet MXCore v2.00) id 1JMfUP-0000ez-Sd
  for me@mine.plus.com; Wed, 06 Feb 2008 08:18:42 +0000
Received: from source ([67.15.127.26]) by exprod5mx212.postini.com ([64.18.4.11]) with SMTP;
Wed, 06 Feb 2008 00:18:40 PST
This evening obvious Spam has appeared and the emails have not apparently been through postini with an example extract

Received: from [200.69.113.49] (helo=corporat200-069113049.sta.etb.net.co)
  by pih-sunmxcore17.plus.net with esmtp (PlusNet MXCore v2.00) id 1JMkHT-0000HU-1s
  for anotherme@mine.plus.com; Wed, 06 Feb 2008 13:25:39 +0000
I am now confused, whether I am on postini, and, if I am why thse later Spam mails are not going through postini.

[#2]

Is it less than a week since you were moved to Postini? If so the following extract from the latest service status announcement about the Postini migrations will explain all:

Quote

Other Notes:- When a customer is moved to the Postini anti-spam platform their mail records are changed to point to Postini instead of our mail servers. As this is a DNS change it can take 24-48 hours before the changes have fully propagated across the rest of the Internet. Hosted domains can take longer to update (up to 7 days). One trick used by spammers involves them sending email directly to the old mail servers. This bypasses the Postini checking so we need to block attempts to do this after migrating each customer. This block is applied 7 days after migration at which point customers may notice a further improvement in the performance of the spam filter.

[#3]

Thank you