Virus-Scanning Applications Based on VSAPI

VSAPI-based anti-virus solutions for Exchange Servers check all email messages received by the server before they are delivered to the clients. Viruses are searched in three modes:

•Proactive

•On-demand

•Background

If the sender address is included into the values list of TrustedEmails variable, the email will not be checked for spam and viruses and will be considered as not being spam or virus.

Proactive scanning

All email messages received by the Exchange Server are queued to be checked by the anti-virus plug-in. All messages in the queue receive the same low priority. If this priority doesn't change then the check proceeds on the «first in, first out» (FIFO) basis.

On-demand scanning

If the priority assigned to the message changes to the high one, that occurs in case a mail client tries to access the message, then it would be processed earlier, because the queue is treated by several threads. The initial low priority of incoming messages guaranties that their check would not interfere the processing of high priority messages.

Proactive and on-demand scanning processes ensure checking all the messages passing the server, the priority system allowing to optimize the server load and clients' waiting time.

Background scanning

In the background scanning mode, messages located in the Information Store are checked, thus the viruses that have passed to the Store before the installation of Dr.Web and the previously unknown viruses in the messages checked before the last updating of virus databases can be detected. The Exchange administrator can start this mode by means of a set of registry keys and manage scanning using the Doctor Web For Exchange Start Background Scanning Task in the Windows Task Scheduler. By default, the task starts daily at 01:15 AM.

For more information on the settings of anti-virus scanning based on VSAPI see Microsoft Exchange Server Anti-Virus Scanning Settings.