[Mimedefang] Filtering idea for stock pump&dumps

[Kevin A. McGrail]

>> This PDF spam is tough.
>
> Greylisting stops quite a bit of it.

FYI, based on what we have confirmed over the past 2 weeks, greylisting is 
causing widespread FPs with Microsoft Exchange 2003 SP2.  In short, 
Microsoft is interpreting 4XX errors as 5XX errors and generating NDRs.

We have logs showing this occurring.  And we completely concur with Yizhar 
Hurwitz about the issues he has posted at 
http://www.webservertalk.com/message1918960.html

For example:

Subject:        Undeliverable: RE: Goco Here
Your message did not reach some or all of the intended recipients.

      Subject:  RE: Goco Here
      Sent:     6/25/2007 10:24 AM

The following recipient(s) could not be reached:

      paulinog@<removed> on 6/28/2007 5:24 PM
            You do not have permission to send to this recipient.  For 
assistance, contact your system administrator.
            <removed.local #4.7.1 smtp;451 4.7.1 <paulinog@<removed>>: 
Recipient address rejected: Policy Rejection- Please try later.>


Making things worse, the NDRs are not always processed immediately.

Anyway, if you are using greylisting, be forewarned that Microsoft seems to 
have known, not quite solved issues.  As they are a LARGE player in the 
email game, I can't recommend greylisting at all for the moment.

Yizhar, if you ever get anything definitive, I'm definitely interested in 
hearing about it.

Regards,
KAM