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Blocking images


When a message is disassembled, the information contained in each component is assigned a classification. This classification is denoted by the ContainerClass attribute.

One of the classifications that may be assigned is Image. This denotes that the information is an image file, for example, a .bmp, .jpg or .gif file.

MAILsweeper can be configured to detect and block images. This is achieved by editing the [Validation] configuration section, to ensure that the DetectImage directive is no longer commented out.

For MAILsweeper the [Validation]section is found in the validator configuration file, VALIDATE.CFG.

That is, change:

[Validation]
;DetectImage=VALATTR

to

[Validation]
DetectImage=VALATTR
The MAILsweeper service will have to be restarted for these changes to come into effect.

If DetectImage is activated for MAILsweeper, any message with an attached image is discarded. The sender of the message is informed accordingly.

You may wish to block or allow images for certain users or groups of users only.

This can be achieved by creating a new AMUcheck rule to name the users and then setting an attribute during AMUcheck validation. This attribute can subsequently be checked in the [DetectImage] section, using a PerformIf directive (to block images for certain users only) or a SkipIf directive (to allow images for certain users only).

For example:



In AUTHFILE.TXT:

RESPONSE allow 
RESPONSE isjunkmail PRIORITY 1
RESPONSE copyadministrator PRIORITY 1
RESPONSE deny PRIORITY 2
RESPONSE No_Images PRIORITY 2

FROM *@* 
  To *@* allow            ;allow everything

FROM	user1@company.com ;List of users not allowed
	user2@company.com ;to send images.
 	user3@company.com
  To *@* No_Images

FINISH

A new AMUcheck rule is defined.

In this example, the rule names the users not allowed to send image files.1 When the addresses of a message match with this rule the <Response> generated by AMUcheck is No_Images.

A new RESPONSE statement is also listed in the first section of the file, to define the No_Images <Response>.

In VALIDATE.CFG:

[AMU]
AuthFile=C:\MSW\CONFIG\AUTHFILE.TXT
If=No_Images, NoImages=TRUE, allow

If the <Response> generated by AMUcheck is No_Images then an attribute called NoImages is created, with the value TRUE.

This is the attribute that is checked by the PerformIf directive in the [DetectImage] configuration section.

The <Response> is then reset to allow. This is the actual <Response> generated by AMUcheck. It allows the message to be delivered normally, assuming no higher priority <Response> is generated by one of the configured plug-in validator instances.

[DetectImage]
PerformIf=NoImages==TRUE
HaveImage=ContainerClass==Image

The value of the NoImages attribute is checked in the [DetectImage] configuration section, using the PerformIf directive.

If the value is TRUE then checking by the [DetectImage] section is performed.

For a similar configuration, using SkipIf to allow images for certain users only, see the blocking executables example on page 5-26.

See the AMUcheck section on page 7-97 for more details. Also, for more details on the If, PerformIf and SkipIf directives, see the Common validator directives section on page 7-102.
 


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1 Checking for images needs only to be performed for these users. This is achieved by including a PerformIf directive in the [DetectImage] section.

msw.support@mimesweeper.com

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