Anti-Spam Techniques at Different ISP Level
Anti-spam techniques can be broken into four broad categories: those that require actions by individuals, those that can be automated by email administrators, those that can be automated by email senders and those employed by researchers and law enforcement officials.
- New Domain
Since spammer's accounts are frequently disabled due to violations of abuse policies and sending emails to non-optin users, they are constantly trying to create new accounts due to the damage done to an ISP's reputation. Due to this kind of behavior of spammers, any new domain which is less than a month old, will not have a good reputation at different ISP levels, and there is a high probability of emails from those domains to get filtered as spam, as this is a known way of spamming. We will not accept such domains unless there is a strong business reason behind it.
- Detecting Spam Based on the Content of the Email
ISP level Web content filtering is followed in almost all nations. Internet traffic is filtered with the help of a blacklist containing Internet addresses (URLs) of sites that are serving illegal Web content, like content related to child pornography. With this type of filtering approach whole domains could be blocked, rather than just the page serving the illegal content, which can also lead to false positives (blocking URLs serving legitimate content) which could cause serious inconveniences for Internet users, especially if the filtering is done at the ISP level. In this perspective, the blocking of domains or IP addresses generates the same type of problems. In order to avoid such problems, the Internet traffic could be filtered dynamically, meaning that the traffic content is analyzed for certain words or images that are blocked if they match a certain signature that is stored in an image signature database.
There are many other factors which are considered for filtering of which three commonly used techniques to block access to Internet sites are: IP blocking, DNS tampering, and URL blocking using a proxy. These techniques are used to block access to specific Web Pages, domains, or IP addresses. Keyword blocking, which blocks access to websites based on the words found in URLs or blocks searches involving blacklisted terms, is a more advanced technique.
- Spam Traps
Spam traps are the email addresses that were never valid, or not in use anymore for a long time, and are used to collect spam. Some blacklists, such as SpamCop use spamtraps to catch spammers and blacklist them.
- DNS Blacklisting
One of the oldest forms of spam prevention is DNS blacklisting, which uses a centralized database to block all emails from a host being used to send spam. The provider of blacklisting services maintains a database adding host entries that are being used to send spam. Although, access to several of these databases are free, here is a tool where you can check if your domain is blacklisted
Spam will remain, knocking it out is a herculean task. The internet is full of options which can be considered for spam prevention however, these techniques offer a fast and effective way to prevent spam. Keeping your customers in mind, always prefer the least aggressive approach to palliate spam.