What are spam filters?
Spam filters are software that's installed on an email server whose sole purpose is to analyze incoming and outgoing emails and, based on a set of rules,
to determine if the email is spam or not. Spam filters can take on many different roles including content filtering, blacklist filtering, maleware filtering, virus detection, etc.
All incoming emails are filtered through a complex set of rules and stamped with a spam score, based on the settings, some email are completely discard and never seen by the recipients.
Some Email Service Providers commonly known as ESP, deploy multiple spam filters from different spam filtering companies in order to reduce the amount of spam their clients receive.
A lot of ESP take the guilty until proven innocent approach, if they never seen mail from you before, that are automatically suspsicious of you. Once you send mail for a while they start to warm up to you.
This is know as IP Warming
, the more consistantly you send the better.
The image below illustrates how an email goes from the sender to the email server, through the spam filter, and finally ends up in either the Inbox, Junk folder, or worst case just simply discarded.
How do spam filters work?
Companies that develop spam filters keep a tight lid on the specifics of how they work. This is a good thing as it keeps the spammers guessing as to how to get around the rules.
Basically, the spam filter programs compare the rules they're programmed with against the email. For example, it's commonly accepted that sending an email with just an embedded image and no text is an attempt to get around the spam filters rules. If the spam filter in question has a rule that says "if this message contains only an image and no text" and it receives an email with an image and no text, that email will get marked as spam.
How do I avoid spam filters?
The actual rules used in spam filters are vast and complex. Every spam filter product has their own proprietary ruleset. However, there are some commonly known and obeyed rules that have been proven effective in the quest to get your emails into your audience's inbox. Here are just a few that we recommend.
- Don't use the word 'test' in the subject of your email.
- Don't embed lots of URLs or images in the body of your email.
- Don't use words like 'sale', 'buy now', 'discount', etc. These words stink of spam.
- Pay attention to your text to link ratio.
- Don't get carried away with bold fonts and colors.
We recommened that you fine tune your marketing email by using the Unlock The Inbox Spam Score Tool
Source: Unlock The Inbox