Configuring the Incoming SMTP Proxy

Use the Incoming SMTP Proxy dialog box to set the incoming parameters of the SMTP proxy. You must already have an SMTP Proxy service icon in the Services Arena.

From the Services Arena:

Double-click the SMTP Proxy icon to open the SMTP Properties dialog box.
Click the Properties tab.
Click Incoming.

The Incoming SMTP Proxy dialog box appears, displaying the General tab.
Modify properties on the General tab according to your preferences.

For a description of each control, right-click it, and then select What's This?. You can also refer to the "Field Definitions" chapter in the Reference Guide.

Configuring ESMTP

ESMTP (Extended Simple Mail Transfer Protocol) provides extensions to SMTP for sending email that supports graphics, audio and video files, and text in various foreign languages. You use the ESMTP tab on the Incoming SMTP Proxy dialog box to specify support for ESMTP extensions (keywords) and for entering AUTH types, which specify various ways of authenticating to the SMTP server.

From the Incoming SMTP Proxy Properties dialog box:

Click the ESMTP tab.

The ESTMP information appears .
Enable the extensions (keywords) you want by selecting their associated checkboxes.
Use the text box provided to enter AUTH types. Click Add.

All AUTH types are supported; DIGEST-MD5, CRAM-MD5, PLAIN, and LOGIN are provided as defaults.

Blocking email attachments

You can use two methods to block email attachments. Either allow only save content types or deny file name patterns. These two methods can be used together to further protect your network from malicious email attachments.

Allowing safe content types

MIME stands for Multipurpose Internet Mail Extensions, a specification about how to pass audio, video, and graphics content by way of email or HTML. The MIME format attaches a header to content. The header describes the type of multimedia content contained within an email or on a Web site. For instance, a MIME type of "application/zip" in an email message indicates that the email contains a Zip file attachment. By reading the MIME headers contained in an incoming email message, the Firebox can strip certain MIME types and admit only the types you want. You define which types of attachments are admitted and which are denied by using the Firebox's HTTP and SMTP proxies.

From the Incoming SMTP Proxy Properties dialog box:

Click the Content Types tab. Specify whether you want to block certain file-name patterns in email attachments by enabling the checkbox marked Allow only safe content types and block file patterns.
If you want to specify content types to allow, click the upper Add button in the dialog box.

The Select MIME Type dialog box appears.
Select a MIME type. Click OK.
To create a new MIME type, click New Type. Enter the MIME type and description. Click OK.

The new type appears at the bottom of the Content Types drop list. Repeat this process for each content type. For a list of MIME content types, see the Reference Guide.

You can use wildcard characters as follows:

To allow content types:
An asterisk (*) matches any string, including an empty string.

To deny file name patterns:
An asterisk (*) matches any string, including an empty string.

A question mark (?) matches any single character.

Denying attachments based on file name patterns

The Content Types tab includes a list of file-name patterns denied by the Firebox if they appear in email attachments. To add a file-name pattern to the list, enter a new pattern in the text box to the left of the Add button. Click Add.

Note that denying a particular attachment does not automatically trigger protocol anomaly detection (PAD) rules. You must specifically add the content type to the PAD rules.

Specifying a deny message

In the Content Types tab, you can enter a message to be shown when a content type is denied--this message is shown to the recipient only and not the sender. A default message is provided. Use the variable %t to add the content type to the message. Use the variable %f to add the file name pattern to the message.

Adding address patterns

Adding address patterns can be useful for reducing spam content. From the Incoming SMTP Proxy Properties dialog box:

Click the Address Patterns tab.
Use the Category drop list to select a category.
Type the address pattern in the text box to the left of the Add button.
Click Add.

The address pattern appears at the bottom of the pattern list.

Protecting mail servers against relaying

Hackers and spammers may attempt to use an open relay to send mail from your servers. To prevent this, disable open relay on your mail servers by restricting the destination to only your own domain.

To further increase protection from mail relaying, modify the SMTP Proxy settings to allow addresses only from your domain. From the Incoming SMTP Proxy Properties dialog box:

Click the Address Patterns tab.
Select Allowed To from the Category drop list.
In the text box to the left of the Add button, enter your own domain.
Click Add.
Save the new configuration to the Firebox.

Select headers to allow

The Firebox allows certain headers by default. These are listed on the Headers tab of the Incoming SMTP Proxy Properties dialog box. You can add more headers to this list, or remove headers from the list. From the Incoming SMTP Proxy Properties dialog box:

Click the Headers tab.

The headers information appears.
To add a new header, type the header name in the text box to the left of the Add button. Click Add.

The new header appears at the bottom of the header list.
To remove a header, select the header name in the header list. Click Remove.

The header is removed from the header list.

Specifying logging for the SMTP proxy

Click the Logging tab to specify whether to log the following:

Unknown headers that are filtered by the proxy.
Unknown ESMTP extensions that are filtered by the proxy.
Accounting and auditing information.

Related topics:

Incoming service guidelines

Defining Firebox Users and Groups for Authentication

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