Do not attempt to configure 3Essentials image scanning if you have already enabled Spam Free Trusted Mail (details here) .

Proceeding with the discussion of image scanning:

Spammers have gotten smarter... they know you're filtering their mail based on keywords... so now they are sending IMAGES that contain their advertisements, knowing that standard text filters can't pick these up.  3Essentials uses image scanning to perform OCR scanning of embedded images to determine if an image contains spam.  This scanning actually takes place at our gateway - we don't block these mails, instead, if the image scanning component thinks an email contains an image that is likely spam, we insert a specific email header to indicate this.  As such, you can then set a CONTENT filter which will take action on emails with this header tag.  You can set it the content filter to do a number of things with these, though the recommended suggestion is to append something to the subject.  The following instructions show you how to set a content filter to append a certain string to the subject of an email suspected by this image scanning component:

• Log into your webmail interface (http://webmail.yourdomain.com)
  • you do not have to continue to use webmail after setting this up, content filters work whether you use webmail or a standalone mail client, however the webmail interface is where they are configured.  There are some limitations, please see the article on content filtering for more details on limitations: Spam Protection: Content Filtering. 
• Put your mouse over SETTINGS which causes a dropdown menu, select MY CONTENT FILTERING
• Click ADD FILTER
• Check the EMAIL HEADERS box, click NEXT
• On this page:
  • Select filter type "AND" (which should be selected by default)
  • In the CONTAINS SPECIFIC WORDS OR PHRASES text box, enter the following text exactly: 3espam-image
  • click NEXT
• You're now on the ACTIONS page, we recommend you:
  • select the PREFIX SUBJECT WITH COMMENT option and add the COMMENT of: **SPAM-IMAGE**
  • click SAVE

Notes:

• You can set the actions to whichever you decide, however we STRONGLY recommend you do not BOUNCE the message, as this causes excessive/unnecessary mail flow.
• You can come in and change this at any time... so perhaps you want to start with the PREFIX SUBJECT option, and once you've decided the scanning meets your needs, you can change it to DELETE.
• You can also then set a rule in your email client to look for **SPAM-IMAGE** in your email's subject, and take action (i.e., move to junk folder, delete, etc...).
• USER-SPECIFIC vs DOMAIN-WIDE... the instructions above covers how to set this filter for a specific user, but you can also set this as a DOMAIN WIDE setting.  Please reference the following KB on content filtering which describes process of setting a content filter for domain-wide usage (all mail users of your domain).
• NOTE: this content filtering option is only available as follows:
  • it is available for customers hosted on: web12, web14, web16
  • it is not available for customers hosted on: web2, web4, web6, web8
    • however, for customers on these servers, you can still utilize this same functionality if your mail client supports custom rules based on information found in the mail header.  For instance. Outlook support Rules based on text found in the header.  Consult your mail client documentation for instructions on how to set a rule for information found in the header, and set a rule for the following text found in the header: 3espam-image