create an event sink that filters and delete emails after being scanned by SAV for exchange
Posted on 2004-04-15
This question is pretty specific to a type of system
SAV for exchange
running on Windows 2000 server SP4
Our problem starts when we are receiving infected emails. SAV for exchange is meant to remove any infected attachment from an email but still delivers the mail to the recipient.
Example : someone outside the company has an infected computer with Netsky. The user doesn't know that his computer is infected but the virus sends itself to everybody in the address book. Usually the subject is random and the text as well.
In the address book, there is one or more addresses of our users from our organisation; so we will be receiving a bunch of infected emails. Fortunately SAV for exchange will scan those incoming emails and remove the attachment. Unfortunately the way SAV works, it will still deliver the mail with the random subject and text and will attach a new file that will be called "Deleted attachment.txt". In that text file there's a description of what happened, basically it will say that the mail contained a virus called Netsky and that the attachment has been removed.
If we have many people outside the company with an infected computer, our users will receive a LOT of those emails with an attachment called "Deleted attachment" ( one of ours is getting up to 800 a day now ).
Now there are many solutions:
1st - first one which is pretty effective is to create a rule on each stations that would delete those type of emails. Unfortunately if the user uses outlook express this won't get effective, and most of all it would take forever to get to everybody stations to create the rules.
2nd - We could use a "perimeter mail app" that would actually do that kind of work but usually these apps tie to an RBL list and filter emails based on those lists which is not totally reliable. Some other of those apps are also pretty expensive
3rd - So by doing some research I noticed that something called "event sink" could be used to filter an email right after it has been scanned by SAV.
The idea would be then to register a new event sink on the mail server ( from what I understand, this would be a VBscript ). The event sink would just delete any email with an attachment called "Deleted Attachment.txt".
Does anyone know how to write such a script ?