A Content Examination definition analyzes the content of messages, looking for matches you provide. It sets the conditions under which a message is considered safe, and what action should be taken if it isn't. Once configured, each definition is applied to either a Content Examination or Content Examination Bypass policy, to control what message flows it should be used for (e.g. inbound or outbound).
Consider the following before creating a policy:
- Content Examination definitions shouldn't be used to manage inbound mail for spam checking, as this is conducted by the Mimecast heuristic scanners.
- Scanning message content is an essential service to ensure Data Leak Prevention (DLP). You can configure specific dictionaries of words and phrases to cater for the following example scenarios:
- Preventing a database from being emailed externally (e.g. a list of customers or confidential product information).
- Protecting a company from losing financial information (banking or credit card details).
- Preventing specific files from being sent or received using a unique file identifier.
- Converting Microsoft Word documents to protected formats.
- Protecting corporate identity by limiting the use of profanity in messages.
- Applying branding for product or service promotions.
- Notifying / copying users when a message triggers a definition.
- Activating email encryption during transmission.
- The use of formatted file scanning can help reduce the incidence of false positives, but at the risk of missing some content. Content examination of the header and subject of a message is separate from the body examination. However the score is cumulative up to the optional limit. If all sections are selected, all sections are scanned, even if the limit is reached prior to examination of the body / attachments. This is to give the sender a more accurate indication of why their message is not acceptable as per the policy.
Configuring a Content Examination Definition
To configure a content examination definition:
- Log on to the Administration Console.
- Click on the Administration menu item. A menu drop down is displayed.
- Click on the Gateway | Policies menu item.
- Hover over the Definitions button.
- Select Content Definitions from the drop down menu.
- Select a Folder in the hierarchy. You cannot create a definition in the Root folder.
- Either click on the:
- New Content Definition button to create a definition.
- Definition to be changed.
- In the Definition Narrative field, provide a description of the definition. This is kept in the archive for messages that have this definition applied.
- Complete the Policy Definitions section as required:
Field / Option Description Description Provide a description of the definition. This is kept in the archive for messages that have this definition applied. Definition Type Specify how the content text is matched. The options are:
- Independent Content Definition: The content is matched directly as listed in the "Word / Phrase Match List" field.
- Reference Dictionary: The content is matched against a predefined set of text entries.This option allows you to create a dictionary that can be referenced by multiple content definitions.
Activation Score Specify a value between 1 and 99 that must be reached before the content definition is triggered. This works by combining the value assigned to text in the "Word / Phrase Match List" field. When the total value of matched text meets this value, the definition is triggered. For example, if the Activation score is set to 6, and there are three words in the "Word / Phrase Match List" field each weighted at 2, and each word appears in the message, the activation score is reached and the definition is triggered.This field is not displayed if the "Definition Type" field is set to a "Reference Dictionary" value. Fuzzy Hash Setting
If selected, you can match files that might not be identical, but do hold a configurable level of similarity. Select the appropriate similarity value from the drop down list (80% probability is recommended). A high probability percentage lowers the chances of false positives.Use the Insert | Fuzzy Hash menu item to add fuzzy hashes to the "Word / Phrase Match List". See the Content Examination Definition: Configuring Fuzzy Hashing page for full details.
- Complete the Scanning Options section as required:
Field / Option Description Word / Phrase Match List
Use the Insert menu item to add a search term to search for that specific text only, or use parameters to meet more complex search requirements. See the Word Phrase Match List Parameter Details section below for further detail.Both the HTML and TXT parts of a message are treated as separate elements when applying a content examination definition. This means that if a trigger word is present once in a message, but is present in both HTML and TXT parts, it scores twice. Similarly if it is present twice in both parts, it scores four times.
Case Sensitive Match If selected, the entered text entered in the "Word / Phrase Match List" field must match the text case in the message (e.g. uppercase, lowercase, or proper case). If not selected, any case is matched.Case sensitivity applies to all terms. Match Multiple Words If selected, a search is performed for repetitions of the text entered in the "Word / Phrase Match List" field. This is used in conjunction with a repetition scoring for the word. For example, an entry of "1:10 notifications" searches for 10 matches of the word "notifications" throughout the message. Scan Subject Line If selected, the message's subject is scanned. Scan Message Headers If selected, the message's message header is scanned. Scan Message Body If selected, the message's message body is scanned. Scan Attachments If selected, the message's attachments are scanned. Additionally, the "Scan Binary Attachment" and "Microsoft Excel Spreadsheet Scanning" fields are displayed. Scan Binary Attachment If selected, documents are scanned for matches based upon the binary data of the file rather than the extracted text content. This option should be enabled for non-text files only (e.g. image / library files).Enabling this option can increase the number of false positives generated by Content Examination policies. Microsoft Excel Spreadsheet Scanning Specify how Microsoft Excel file attachments are scanned. The options are:
- Raw Files: Scans the file's contents as recorded in the .XLS / .XLSX source file.
- Formatted Files: Scans the file's contents as it would be seen by a Microsoft Excel user. This evaluates the formatting of each cell independently and searches for possible matches across multiple cells.
- Complete the Policy Override Options of the "Inbound and Outbound Settings" section as required:
Field / Option Description Enable Inbound and Outbound Checks If selected, the fields / options listed below are displayed. These can be used to protect against unsafe content in both inbound and outbound traffic. If unselected, only inbound traffic is checked using the settings in the "Scanning Options" in step 10. Policy Action Specify the action to be applied by the definition. The options are:
- None: No action is taken.
- Hold for Review: The message is sent to the hold queue, and not delivered to the recipients.
- Delete: The message is purged from the delivery queue, but retained for auditing purposes. It is referenced as a hard bounce in the message's delivery information. See the Bounced Messages page for further details.
- Bounce: The message is rejected, and not delivered to the recipients. A notification is sent with the reason "Message bounced due to Content Examination Policy". See the Bounced Messages page for further details.
Hold Type If "Hold for Review" is specified as the "Policy Action" field, this option specifies who can see the message via a Mimecast end user application. The options are:
- User: Users can see the message in their Personal On Hold view.
- Moderator: Moderators can see the message in the Moderated On Hold view. The group of moderators is specified in the "Moderator Group" field.
- Administrator: Messages can be viewed by administrators only.
Moderator Group Specify a group of moderators who can access messages in the Moderated On Hold views via a Mimecast end user application. Content Preservation (Days) Specify how long the message remains in Mimecast before being purged. This also applies to messages held in the hold queue once the message expires from the queue.Leaving both options at 0 (days) doesn't affect the default content retention period set on your account. Metadata Preservation (Days) Document Policy If Document Services is enabled on your account, you can strip metadata from documents before they leave your organization, and convert documents to PDF, ODF, or other Word versions. This option also allows you to apply document services definitions to messages based on their content. Disable Document Services Disables Document Services if it is enabled on your account. Assign to Smart Tag Assigns a Smart Tag to the message. This field is only available if the "Disable Smart Tags" option is disabled. Disable Smart Tags If selected, the ability to add a smart tag to a message is disabled. Delivery Route Specify the delivery route to deliver messages to the next mail server. For example, if the message contains the address firstname.lastname@example.org, deliver it to the Call Center email server. Secure Delivery Use the Lookup button to apply a Secure Delivery Definition to add additional security to the message's delivery. Encryption Mode If the definition specified in the "Secure Delivery" uses TLS, specify the encryption mode to use. The options are:
- Strict: This is a trust enforced mode, and requires a public certificate. This is the recommended option.
- Relaxed Mode: This requires a self-signed certificate.
Attachment Strip and Link If selected, the attachment(s) are removed before the message is delivered. The message contains a notification of the removal in the message's body, and a link is included to download the attachment(s). Secure Messaging Override Use the Lookup button to apply a Secure Messaging Definition to send the message via Mimecast's Secure Messaging functionality. Group Carbon Copy Use the Lookup button to send a copy of the message to a group of users. Stationery Override Use the Lookup button to apply a Stationery Layout that overrides an existing stationery policy. For example, if the phrase "new product" is in the message, apply a Stationery Layout that promotes the product. Disable Stationery If selected, stationery is not applied to any message.
- Complete the Notification Options of the "Inbound and Outbound Settings" section as required:
Field / Option Description Notify Group Use the Lookup button to select a group of users to be notified that action must be taken on the message. Notify (Internal) Sender Notifies the internal sender if an outbound message triggers the definition. Notify (Internal) Recipient Notifies the internal recipient if an inbound message triggers the definition. Notify Overseers Notifies the Content Overseers to notify them that a message has triggered the definition. Notify (External) Sender Notifies the external sender if an inbound message triggers the definition. Notify (External) Recipient Notifies the external recipient if an outbound message triggers the definition.
- Complete the Journal Settings section as required. This section is only available if you've Targeted Threat Protection: Internal Email Protect enabled on your account. When configuring your journal settings, consider our recommended best practice settings. These are based on commonly used configurations, and can provide an optimal solution to protect you against targeted attacks via attachments.
Field / Option Description Enable Journal Check If selected, the fields / options listed below are displayed. These can be used to protect against unsafe content in journaled traffic. User Mailbox Action Select the action (or fallback action) to take on the user's mailbox if a message containing unsafe content is detected. A "User Mailbox Fallback Action" is only applied if we're unable to check a URL.
In non-Exchange environments automatic remediation is not supported. However if a support journal connector is used, you can leverage detection, and through these alerts perform manual remediation.
- None: No action is taken on the user's mailbox, and the message is delivered to the recipients.
- Remove Message: The message containing unsafe content is removed from the user's mailbox.
User Mailbox Fallback Action Enable Notifications Enables a group of users to be notified, as well as the internal sender / recipient, when a message containing unsafe content is found. If selected, the "Notify Group", "Internal Sender", and "Internal Recipient" fields are displayed. Notify Group Click on the Lookup button, to select a group of administrators to receive notifications of any messages containing unsafe content. Internal Sender If selected, a notification is sent to the message's internal sender, if there are any messages containing unsafe content. Internal Recipient If selected, a notification is sent to the message's internal recipient, if there are any messages containing unsafe content.
- Click on the Save and Exit button.
Word Phrase Match List Parameter Details
Once the words or phrases have been entered into the list "Word / Phrase Match List" field, additional criteria can be added to make the content matching more specific.
The use of formatted file scanning can help reduce the incidence of false positives but at the risk of missing some content. Content examination of the header and subject of a message is separate from the body examination. However, the score is cumulative up to the optional limit. If all sections are selected, all sections are scanned, even if the limit is reached prior to examination of the body / attachments. This is to give the sender a more accurate indication of why their message is not acceptable as per the policy.
|Weight||The line must begin with the required score for that particular word or phrase.|
|Max Score||Allows you to set the maximum number of occurrences that a word in the message should trigger the definition. For example, if an entry of "1:13 index fish" is specified, Mimecast would match up to 13 instances of the word "fish", with each instance scoring 1. If "1:" is entered before the search term, there is no upper limit to the score. This scoring is only used if the option "Match Multiple Words" is enabled. The combined score of the individual Weights is tallied and matched to the Activation Score, with the definition only triggered once the Activation Score is reached.|
|Conditions||Allows you to use the operators “required” and “exclude”. Add the word required if the match term is specifically required for the policy to trigger. If a required item is not found, the weight is set to zero and no further scoring takes place. If the word exclude is added after the weight, and the match term does exist, the weight is set to zero and no further scoring takes place. Required and exclude terms should be placed in the first line of the search term list.|
|Search Text / Phrases||Enter single words or phrases, enclosing multiple words in quotation marks (e.g. “a phrase”).|
|Regular Expressions||Proceed the regular expression with “regex”. Regular expressions can be used to detect structured strings like Social Security Numbers or Credit Card Numbers in emails.|
|MD5#||Enter the “#” symbol at the beginning of the line (or following the score if relevant) followed by the MD5 code of the attachment. The MD5# is a unique reference given to specific file contents. |
If the attachment is known to Mimecast (i.e. Mimecast has previously processed the attachment), this checksum is located in the Transmission Data when viewing the email delivery details.
|Preconfigured Reference Dictionaries||Use the Insert | Reference Dictionary menu item to select a Reference dictionary. The entry will begin with the word “reference”, followed by the internal Mimecast reference code and dictionary name. Reference Dictionaries can be created manually, or a predefined Mimecast Managed Reference Dictionary (MMRD) can be selected.|
|Comments||Comments can be inserted by using a hash symbol (#) at the beginning of the line. These are ignored when examining the message for matches.|
Word Phrase Match List Parameter Examples
|Weight : [ maxscore ] [ search text ]||4:1 “Company Confidential”|
|Weight [ required ] [ search text ]||1 required “Project X”|
|Weight [ exclude ] [ search text ]||1 exclude “Tax exemption”|
|Weight [ regex ] [ regular expression ]||10|
|Weight [ # ] [ MD5# ]||1 hash 9EBD30E761ED4FF770A90DDBD5CB4190 Confidential.PDF|
Configuring a Content Examination Policy
To configure a Content Examination policy:
- Log on to the Administration Console.
- Click on the Administration toolbar button. A menu drop down is displayed.
- Click on the Gateway | Policies menu item.
- Click on Content Examination. A list of policies is displayed.
- Click the New Policy button to create a policy
- Click on the policy to be changed.
- Complete the Options section as required:
- Complete the Emails From and Emails To sections as required:
Field / Option Description Addresses Based On Specify the email address characteristics the policy is based on. This option is only available in the "Emails From" section. The options are: Option Description The Return Address (Mail Envelope From) This default setting applies the policy to the SMTP address match, based on the message's envelope or true address (i.e. the address used during SMTP transmission). The Message From Address (Message Header From) Applies the policy based on the masked address used in the message's header. Both Applies the policy based on either the Mail Envelope From or the Message Header From whichever matches. When both match the specified value the Message Header From will be used. Applies From / To Specify the Sender characteristics the policy is based on. For multiple policies, you should apply them from the most to least specific. The options are: Option Description Everyone Includes all email users (i.e. internal and external). This option is only available in the "Emails From" section. Internal Address Includes only internal organization addresses. External Address Includes only external organization addresses. This option is only available in the "Emails From" section. Email Domain Enables you to specify a domain name to which this policy is applied. The domain name is entered in the Specifically field. Address Groups Enables you to specify a directory or local group. If this option is selected, click on the Lookup button to select a group from the Profile Group field. Once a group has been selected, you can click on the Show Location field to display the group's path. Address Attributes Enables you to specify a predefined Attribute. The attribute is selected from the Where Attribute drop down list. Once the Attribute is specified, an attribute value must be entered in the Is Equal To field. This can only be used if attributes have been configured for user accounts. Individual Email Address Enables you to specify an SMTP address. The email address is entered in the Specifically field.
- Complete the Validity section as required:
Field / Option Description Enable / Disable Use this to enable (default) or disable a policy. If a date range has been specified, the policy will automatically be disabled when the end of the configured date range is reached. Set Policy as Perpetual If the policy's date range has no end date, this field displays "Always On" meaning that the policy never expires. Date Range Use this field to specify a start and / or end date for the policy. If the Eternal option is selected, no date is required. Policy Override This overrides the default order that policies are applied. If there are multiple applicable policies, this policy is applied first unless more specific policies of the same type are configured with an override. Bi-Directional If selected the policy is applied when the policy's recipient is the sender, and the sender is the recipient. Source IP Ranges (n.n.n.n/x) Enter any required Source IP Ranges for the policy. These only apply if the source IP address used to transmit the message data, falls inside or matches the range(s) configured. IP ranges should be entered in CIDR notation.
- Click on the Save and Exit button.