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AVG Linux Email Server / User Manual
19
5. E-mail Scanning
5.1. General Principles
The
AVG for Linux E-mail Server service responsible for e-mail scanning runs as
a set of memory resident daemons. These daemons are identical preforked
processes bearing the
AVG Anti-Virus scanning kernel and interface for scanning
the e-mail content fetched by
AMaViS, Qmail-Scanner or respective commercial
e-mail server.
The number of e-mail scanning daemons can be specified in the
AVG for Linux E-
mail Server
configuration file (see chapter 8.3 Configuration File/AvgDaemon for
detailed information on this issue). The default number of daemons is
2, possible
values range across all non-negative integers. Increase the number of daemons for
very busy servers to accelerate the e-mail scanning by introducing a higher level of
parallel processing. A general rule of how to regulate the number of daemons can
not be formulated exactly because the scanning performance widely varies
according to the particular system configuration, other services running and
software installed.
Note: Be careful when changing the number of daemons; its excessive increase can
cause temporary service failure problems after restarting or sending another signal
to the
AVG for Linux daemons (for example when the virus database is updated
and being reloaded by scanning daemons)!
The
AVG for Linux E-mail Server e-mail scanning service is bound to the IP
address that is also specified in the respective section of the configuration file
(127.0.0.1 by default). The address must be the same as the one the mail transport
agent is bound to. The default port which the daemons are listening on is 55555. If
necessary, this value can be changed in the configuration file as well.
AVG for Linux E-mail Server does not support direct configuration of actions to be
performed after virus detection and/or suspicion in the processed e-mail. These
features are covered by the e-mail server agent and/or respective mail content
scanner. Please refer to the documentation of your e-mail server and
AMaViS or
Qmail-Scanner for detailed information.
5.2. Performance and Resource Usage
Adding virus scanning to an e-mail server can slightly increase the resource usage
of the server for the open source mail transport agents (these are
sendmail,
postfix, qmail, exim). As both of the e-mail scanner wrappers (AMaViS and
Qmail-Scanner) are written in Perl instead of low-level C, some amount of memory
and other system resources is required to make the scanning processes run in order
to scan the e-mail server traffic efficiently. However, the real additional system load
depends on many factors (such as the size of e-mail float, the number of memory
resident processes and so on) that can be effectively optimized by the system
administrator.
It is suggested that you look at how many simultaneous SMTP sessions you are
willing to run on your system. Each SMTP session can claim a certain number of
AVG for Linux E-mail Server virus scanning daemons. The estimated amount of
memory to be used by all the scanning processes per SMTP session is about 5-6 MB.
It is strictly recommended to take this into the account when planning a server
policy and usage management strategies.