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Email Filters:  Overview

Support: Email: Filters Overview

Cotse's email filters fall into two general classes: those that are designed to help you conveniently sort and manage your non-spam email and those that are specifically designed to reduce spam or objectionable material from your inbox.

Our range of filters enable you to block ALL email other than what you specifically allow (see Highly Restrictive , below), create lists of individuals and domains who are specifically blocked (see Blacklisting in that section), use spam-blocking filters and systems such as Bayesian filtering and SpamAssassin (see Spam Filters , below), block mail that arrives with potentially infected attachments (see Block Potential Infections, below), or sort your mail and tag it for easy reading and organization (see Filtering Mail and Sorting Mail, below).

Instructions for enabling each type of filter and creating your rules can be found within the web interface by clicking on "Options" at the top of the screen and then clicking on the type of filter you wish to explore or use.

Note that when constructing your own rules, you should consider the order in which Cotse's filters are applied to your email as the filters are applied sequentially. A listing of the order in which the filters are applied is provided here.

Highly Restrictive Rule-Based Filters

Filters That Block Potential Infection

Cotse offers the following two systems for those who want to essentially bar all email other than from selected senders: Note that you are not required to use either of these systems; they are simply available to you as part of Cotse's suite of filtering options.

Goldlist Sender(s) - One of Cotse.Net's unique filters is the Goldlisted Senders list -- a list you create by entering the email addresses of those from whom you will accept email. You can goldlist individual senders, entire domains, or even particular extensions (such as .biz, .uk). Mail received from addresses on your goldlist senders list will get delivered to your Inbox while all other messages will be delivered to your Trash folder, deleted from the server, merely tagged with an X-Goldlist tag in the header, or rejected, at your option.

Goldlisting Senders is a great idea for those who only want to hear from selected senders or domains (such as a workgroup or specific friends and family), or for parents who want to be able to establish permissions for their children's email correspondents. Goldlisting senders in conjunction with deleting all email from those not on the goldlist disables all other filters described below. As long as the mail is from a sender on your goldlist and you haven't killed your alias (see below), the mail will be delivered to your Inbox.

Need to add someone or delete them from the Goldlisted Senders? No problem - your Goldlist can be easily edited with the webmail interface.

Subject-Line Password Protected Email - Instead of creating a Goldlist for Senders, you may wish to use subject-line password protection for your incoming email. In this system, you create a password (NOT your login password) that you give out to selected friends, family or colleagues. Tell them that they must include that password in the subject line of any email to you or their mail will not be received.

With subject-line password-protected email, messages that contain the password in the subject line will be delivered to your Inbox and other filtering rules will be disabled.

Any messages without the password in the subject line will be delivered to your Trash folder, deleted, or rejected, at your option. You can disable subject-line password protection at any time or change the password phrase and start again, if need be.

Handling Inline HTML - Web bugs, advertising images, and a lot of spam comes with html or web pages embedded in the email. By forbidding html, you can reduce spam and disable web bugs that are often embedded in email as a way of letting the sender know the message was viewed.

Handling Attachments - Worms, trojans, and viruses are an increasing problem, but you can reduce your risk of getting infected by forbidding emails with certain potentially dangerous attachments. The attachments management options page includes a checklist with all of the executable file types. You can ban some kinds of attachments, or all types of attachments on the list (the default setting is to ban all potentially dangerous attachments). You can also add your own file types to the list of blocked attachments. Note that if you forbid some or all attachments, all messages containing such attachments will be delivered to your Trash folder, deleted, or rejected, at your option.

Unsafe Image Rules - You can set up rules for handling potentially unsafe images and whether they are displayed in your webmail. You can select several different options defining who will be considered trusted. You can also pick from several fields in the headers and specify a search string (such as the sender's address) which, if found, will allow the images in your messages. With this option, you can allow some people you trust to send you potentially dangerous image files while forbidding others.

Intermediate Restrictive Filters

Spam Filters

Banned Vocabulary List - With this form of rule-based filtering, you can maintain your own library of forbidden words or phrases and use it to block offensive emails from ever reaching your Inbox. Any messages with words or phrases listed on your ban list will be delivered to your Trash or Spam folder, deleted, or rejected, at your option. By setting your filter rules to delete messages with banned vocabulary and not to notify you, you will never see the message or any of its offensive text at all.

In addition, you can use this feature to search for headers that are added by SpamAssassin, so you can pick and choose which types of messages to block based on the results of tests performed by SpamAssassin (requires enabling of Spam Assassin).

Establishing a banned vocabulary list is easy. Simply copy and paste, or type in the text you wish to ban on the options page for banned vocabulary. You do not need to worry about upper and lower case letters, simply add whatever you think will stop a particular type of message from getting through. This technique can be very helpful if you are not using very restrictive filters, as it enables you to eliminate some spam based on keyword or even part of a keyword (such as "viag" to block some of the variations of spellings for viagra, which is currently popular in spam).

Blacklist Sender - Cotse filters give you the option to blacklist a specific sender by username, or to blacklist a specific email address, an entire domain, an entire extension (like .biz), and/or an entire country (like .ch or .ru). Blacklisting will block any email from that address or specified domain from being delivered to your Inbox.

Blacklisting Sender(s) is a useful tool for preventing specific individuals, specific organizations, or entire domains from contacting you via email. Any time you receive an email you don't want, you can blacklist the sender or domain for the future by simply clicking a link while the email is open in your webmail interface (i.e., when you are looking at the message page). You can also manually edit your blacklist to add or delete particular senders or domains. All mail from blacklisted sources will be delivered to your Trash folder, deleted, or rejected, at your option.

Goldlist Your Email Aliases - Goldlisting one or more of your own email aliases enables to you to receive email addressed to only those aliases, while email to all your other aliases is either deleted, sent to Trash, or rejected, at your option. Goldlisting email aliases is particularly useful for those who own their own domain and only wish to receive email for particular aliases at that domain while rejecting all others.

Unlike the Goldlist Sender filter, however, goldlisting an alias does not automatically deliver all email to the goldlisted alias to your inbox. Rather, it acts as a gateway, and allows email addressed to your goldlisted alias(es) to pass through the gateway and then go through any other filters you may have created or enabled.

Whitelist Sender- If you do not have the Goldlist Sender option activated, whitelisting a sender's address or domain will guarantee delivery to your Inbox regardless of any other rules you have set up. This is useful, for example, if you need to blacklist an entire domain but you still want to receive email from one person (or a number of individuals) at that domain. It is also useful for defining a circle of friends to whom you want to give the ability to email you even if they should happen to use a word that might be in your banned vocabulary list.

Any email received from addresses listed in the Whitelist Sender list will be automatically delivered to your Inbox. For your convenience, users or entire domains can be whitelisted by clicking on a link on the message page, or by manually entering the information on the whitelist management page in your webmail interface.

Whitelist Destination Address - This form of Whitelisting guarantees that messages sent to specified addresses (such as the custom aliases you create to subscribe to mail lists) will be delivered to your Inbox, regardless of any other rules for restricting email.

Cotse gives you a variety of filters to help you reduce spam, dangerous messages (those containing viruses, worms, etc.) or objectionable materials from ever reaching your inbox. Whereas most systems deliver mail to your inbox and then apply filters, Cotse's filters are server-side, i.e., they are applied before the mail ever gets to you. Note that you do not need to choose among spam filtering methods: you can enable any or all of the following:

Bayesian Filtering - Bayesian filtering uses a statistical analysis of the incoming messages based on your own database of information that describes spam and non-spam messages. With this type of filtering, you train it to recognize what you consider valid email and what you consider spam. In time your filter will adapt to suit your particular needs. This is currently the hottest thing in Spam filtering.

SpamAssassin - SpamAssassin will score the incoming email based on its content to determine whether the message is likely to be spam, and if so, it will be delivered to your Spam folder, deleted, or rejected, at your option. If you suspect a friend's mail might land up being coded as "spam," you might wish to set your options for delivery to the "Trash" or "Spam" folders so you can skim them to make sure no "real" email got rejected (alternatively, you may wish to use the Whitelist Sender option to insure your friend's email reaches your Inbox).

DNSBLs (DNS Blacklists) - Cotse provides a list of externally generated spam filtering lists. If you wish to use one of these lists to scan your incoming mail, simply enable the list(s) of your choice. In our experience, using SpamAssassin in conjunction with some "Banned Vocabulary" usually works to catch and delete most spam.

Want to use a DNSBL that's not on our list?  Email helpdesk at and if it's publicly available, we'll add it for you.

SpamCop - SpamCop is a free service that greatly assists in finding the true source of the spam and helps in letting the proper people know about the abuse. To use it, you must get a SpamCop authorization code. There is a free sign up page you can use to sign up for an account. Once your account is set up, you can enter your authorization code on our SpamCop page, and then use the easy link to report spam to SpamCop. Please read the caution on our SpamCop page, however.

Kill Aliases - The Alias Killfile prevents messages that are sent to certain aliases (e.g., from being delivered. This is useful for aliases that have become spam traps - simply list the alias in the Kill Alias page of your webmail interface, and any mail sent to it will be delivered to your Trash folder, deleted, or rejected, at your option.

Filters That Help You Redirect Mail

Filters That Help You Sort Mail

Cotse has a number of filters to help you forward mail to other destinations. For mail that is not Sender-Goldlisted, Subject-Line Password-Protected, or Sender-Whitelisted, you can use the Mail Filters option to create rules to filter mail to other addresses. The filters can detect information in the header and/or in the body of the email, allowing you to filter it to your cell phone, your PDA, or another email address or account. Two examples of how you might use these filters are:

Filter Destination to Alternate Address - forward email based on the destination address in the envelope of the message. This is useful if you wish to give people a Cotse address and not your main ISP account or address. By configuring this section, mail sent to you at a Cotse identity can be redirected or forwarded to another address of yours.

Filter Sender to Alternate Address - Want to forward all mail from one individual or domain to another email address or account? You can do that by using this feature.

Cotse also has filters that enable you to sort your incoming mail. Two examples follow:

Filter Destination To Alternate Folder - Sort your incoming mail into folders based on the destination address in the envelope of the message. This is a convenient feature if you have used an alias or identity to sign up for a mail list. Any mail that comes in directed to that identity can be quickly sorted into a folder for that mail list that you create in Folders.

Filter Sender To Alternate Folder - Want to sort all mail from one individual or domain to a particular folder? Use this feature in conjunction with creating a new folder for that individual or domain's mail.

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