In my previous article – "Filtering E-mail by World Regions in Exchange Server 2003", I wrote about a way to block e-mail originating from specific countries. Although this can be done at the Exchange server level, sometimes, in cases where a user wants to block certain areas of the world from sending him or her spam or other unwanted e-mail, he or she can turn to the client side of the messaging infrastructure.
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Using Outlook 2003 SP2 or Outlook 2007's Junk Email filter options, you can block e-mail by the top level domains by country (.NG, .CN, .CZ, .HK, and so on) and encoding (character sets).
As noted on my previous article, originally, most spamming e-mail servers were hosted in the United States, but with the adoption of several anti-spam laws many spammers were forced to move their operations to countries with fewer controls and rules to host their operations. Today, countries such as China, Korea, Russia, Vietnam, and Brazil are fast becoming sources of spamming mail servers. Naturally, countries with the highest number of spammers operating within their networks are usually those with poor or non-existent spam laws.
E-mail traffic received from places where an organization has no interest will likely be spam, and can be easily accomplished by using either Exchange 2003's connection filtering capabilities alongside with a good DNSBL server (see "Filtering E-mail by World Regions in Exchange Server 2003"), or by using a good 3rd-party anti-spam software or appliance.
Since in Outlook 2003 SP2/Outlook 2007 you can only block e-mail by the top level domains by country and not by IP address ranges, this will not be as effective as using a good 3rd-party anti-spam application that has more complex capabilities. The reason for this is that many spammers do not use country domains on the Mail From e-mail addresses they fake, and the Outlook Junk filter can only look at the e-mail's header and it cannot perform a true investigation on the real sources of that e-mail.
Also, filtering spam by encoding may remove more spam from your mailbox, but again, this is not as effective as a good junk mail filter.
To set these options follow these steps:
1. Open Outlook 2003 or 2007
2. Click Actions --> Junk Mail Options
3. In the Junk Mail Options window, click on Blocked Top Level Domain List
4. In the Blocked Top Level Domain List window, scroll and select any country you wish to block, based upon the top level domain name assigned to that country. For example, if you wish to block Nigeria, click and select NG (Nigeria).
5. Click Ok.
6. Back in the Junk Mail Options window, click on Blocked Encoding List.
7. In the Blocked Encoding List window, scroll and select any encoding type you wish to block. Make sure you only block encodings for countries or regions you do not do business with. In English speaking countries, much of the legitimate email will use US-ACSII or Western European. I also add Hebrew to the list of NON blocked encodings.
8. Click Ok all the way out.
As in my previous article, note that no matter how good Outlook's junk mail filter looks, a decent 3rd party anti-spam filter will do a better job of filtering out all of the spam, regardless of the country of origination. In any case, most organizations will opt to perform most of the junk mail filtering at the server, gateway, or mail relay level, leaving the user with some management capabilities (such as adding or removing senders from personal white lists or black lists, and some ability to look at the blocked items to see if any of them is of any importance to the user).