E - Mail
From Wiki@Commgate
Contents |
Antispam
Overview
| Antispam | Information |
|---|---|
| Description | Antispam for mail servers. |
| Package Name | cc-spamassassin |
| Configuration Page | Software > Mail > Antispam |
The antispam software works in conjunction with your mail server. The software identifies spam using a wide range of algorithms on e-mail headers and body text. The CommGate Server also includes Greylisting and additional Blacklists -- both are effective tools that can be used to detect spam.
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Configuration
Discard Policy (Block Policy)
If you want to discard spam before it reaches mailboxes, you can configure the mail discard policy. For example, you can discard spam marked with high probability (or higher) by using this tool.
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Subject Tag
- Use Subject Tag - enable/disable e-mail subject tag when e-mail is marked as spam
- Subject Tag Threshold - spam score required to trigger a change in the e-mail subject
- Subject Tag - the subject tag to use when e-mail is marked as spam
A subject tag can be added to messages marked as spam. For instance a spam message with the subject "Premier Invest0r Rep0rt" will be transformed into "[SPAM] Premier Invest0r Rep0rt". This feature makes it easy for end users to identify and filter spam.
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Image Processing (OCR)
Enabling Image Processing will improve the spam identification rate for spam messages containing images. Using OCR (Optical Character Recognition), antispam engine will convert images to text and perform analysis on the word content of the image.
White and Black Lists
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Whitelists and Blacklists
- White List - a list of e-mail addresses that should never be marked as spam
- Black List - a list of e-mail addresses that should always be marked as spam
The antispam engine includes both white and black lists. The white list is used to mark e-mail addresses that send non-spam, while the black list is used to mark e-mail addresses that are known spam.
Among others, newsletters and legitimate e-commerce e-mail can sometimes be marked as spam. The e-mail addresses for these messages can be added to the white list to prevent the message from becoming marked as spam.
E-mail addresses in the white and black lists can use the * wildcard character to match any characters. For instance, *@example.com and *.gov will mark all e-mail from the example.com and .gov domains.
Improving Effectiveness
Spam Training
You can improve the effectiveness of the antispam engine by following the instructions here.
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Greylisting and Blacklists
The CommGate Server also includes Greylisting and additional Blacklists -- both are effective tools that can be used to detect spam.
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Links
SpamAssassin website
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Antispam - Dspam
Overview
| Antispam - Dspam | Information |
|---|---|
| Description | Antispam for mail servers. |
| Package Name | cc-dspam |
| Configuration Page | Software > Mail > Antispam - Dspam |
The Dspam antispam system tracks e-mail by mailbox. In other words, the antispam system bases its decisions on individual spam databases for each user on the system.
Warning! Since the Dspam antispam solution requires specific details about mailboxes and aliases, the software is not available on systems configured as a mail gateway. For example, a message destined to sales@example.com forwarded to an Exchange server may end up in Mary and David's mailbox. It is not possible for the Dspam system to determine this information in mail gateway mode.
Configuration
Signature Location
The antispam system tracks important elements and statistics on every e-mail message that you receive. This information is then stored as a "signature" -- basically a unique identification number. To train the antispam system (see next section), this signature must be included in an e-mail. You can track these signatures either in the body of the message, or in the message header.
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Headers
- advantage: does not clutter the body of e-mail messages
- disadvantage: message must be forwarded as an attachment to train the antispam system
Body
- advantage: message can be forwarded (no attachment) to train the antispam system
- disadvantage: spam signature clutters the body of e-mail messages
Subject Tag
Select the subject tag used to mark any messaged deemed to be spam.
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Improving Effectiveness - Spam Training
You can improve the effectiveness of the antispam engine by following these instructions.
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Links
Antispam - Training
Overview
You can improve the effectiveness of the antispam systems on your CommGate system by identifying:
- Messages that were spam, but not identified as such
- Messages that were innocent, but identified as spam (false positive)
With a week or two of diligent training with these messages, you can expect to see a more effective antispam engine.
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Installation
At least one of the antispam engines must be installed on your system.
- SpamAssassin
- Dspam
Training
There are two ways to train the antispam systems on your CommGate Server: webmail and mail-forwarding.
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Webmail
Training the antispam system via webmail is simple and more effective. Simply select the messages that you wish to process and press either the Report as Spam or Report as Innocent buttons (see screenshot). You will then be shown a confirmation message before the actual processing takes place.
E-mail Forwarding
Training via e-mail forwarding is not as effective since information is lost when you forward a message. If you decide to use this method, there are two e-mail addresses used for training:
- train.notspam@example.org -- e-mail address for messages incorrectly identified as spam
- train.spam@example.org -- e-mail address for spam that was not identified as such
In order to use this style of spam training, messages must be forwarded as an attachment (see screenshot).
Links
Antivirus
Overview
| Antivirus for Mail Servers | Information |
|---|---|
| Description | Antivirus for mail servers. |
| Package Name | cc-clamav |
| Configuration Page | Software > Mail > Antivirus |
The antivirus system scans mail messages as they pass through your mail server.
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Configuration
Mail Policies
When configuring the antivirus system, you must make some mail policy decisions. There are three types of policies available:
- Bounce bounce the e-mail
- Discard - silently discard the e-mail
- Pass Through - send e-mail with warning (original sent as an attachment)
Virus Detected Policy
When a virus is detected, you can choose to either discard the message, or pass the message through. We recommend discard mode for most installations.
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Banned File Extension Policy
The antivirus software not only performs virus scanning, but also manages file attachment policies. Certain types of file attachments are prone to viruses. The ability to block attachments by file extension is another layer of security for your mail system.
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Banned File Extensions
Select the file extensions that you wish to ban from going through your mail system. Both internal and external mail are checked.
Links
Filters / Greylist
Overview
| Greylisting and Filters | Information |
|---|---|
| Description | Greylisting and filters for mail servers. |
| Package Name | cc-filters |
| Configuration Page | Software > Mail > Filters |
Greylisting and mail filters are extra tools to prevent spam from reaching your users' mailboxes.
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Installation
If you did not select this module to be included during the installation process, you must first install the module.
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Configuration
Greylisting
Greylisting can dramatically reduce the amount of spam reaching your mailboxes. When the service is enabled, a mail message that is not recognized will be gently rejected. If the mail message is legitimate, the sending mail server will re-attempt subsequent deliveries and the CommGate server will then accept it. For the most part, spammers do not bother with the second delivery attempt and this results in less spam. The parameters that you can use to fine tune the greylisting engine are described below.
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Status
State of the greylisting engine.
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Delay
The amount of time that must pass before a subsequent delivery attempt is allowed.
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Data Retention Time
The greylisting engine keeps track of both mail servers and sender e-mail addresses for a specified amount of time (default is 35 days). If messages from validated sender or server arrives, the greylisting engine will accept delivery on the first attempt. For example, if dave@example.com sends an e-mail to one of your users on a weekly basis, only the very first mail message is delayed. All subsequent messages are delivered automatically since dave@example.com has been validated.
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Blacklists
CommGate provides extra mail blacklists to protect against spam. You can enable or disable this blacklist at any time.
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Links
Maildrop
Overview
| Maildrop | Information |
|---|---|
| Description | Fetchmail/maildrop software to fetch mail from external servers. |
| Package Name | cc-fetchmail |
| Configuration Page | Software > Mail > Maildrop |
The fetchmail package can conveniently retrieve mail from other servers allowing the 'centralization' of e-mail on a single server.
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Installation
If you did not select this module to be included during the installation process, you must first install the module.
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Configuration
Any number of servers can be added to the maildrop list using the "Add Maildrop Entry" form. The interval polling time can be configured from 1 minute up to 3 hours.
Server - The server name. For example, gmail.com.
Protocol - The server protocol. Currently, POP3, IMAP and APOP protcols are supported. If you do not know the protocol, you can have the system auto-detect by selecting 'auto'.
Username - This is the username on the source server.
Password - This is the password on the source server.
Local User - This is the username of a mail account configured to receive mail on the server you are configuring.
Keep On Server - Enable this checkbox to leave a copy of the mail on the server.
Active - Enable this checkbox to start polling the remote server for mail to fetch.
Note: As with any other POP3 or IMAP connection, your username and password for the mail account on the destination mail server will be passed in clear text.
Troubleshooting
Have a look at the system logs if you are having problems. The fetchmail daemon logs to /var/log/maillog. Ignore any entries you see similar to:
Server CommonName mismatch: localhost.localdomain != mail.commgate.net
This entry is a result of fetchmail attempting to use SSL for authentication.
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