Many business owners often wonder why email messages go to spam. In my previous entry, I shared seven sure-fire ways on how to get your email messages to the spam folder. Apparently, small business owners want their messages to go to the inbox. In this entry, I’ll explain how spam filters work so you understand them. This is a great reference for any marketer so they understand how spam filters function.

The goal of email marketing 2.0 is tailored in such a way to not worry about spam filters. We know that; however, it’s important to consider the levels of filters their recipients have so you see what you’re up against to get the message in the inbox.

We’re not alone. Every Email Service Provider (ESP) provider including Constant Contact, iContact and AWeber all face the challenge of getting their users’ messages to the inbox. While the ESP maintains the bulk of the responsibility in getting messages there, content of the emails are crucial to consistently have the message hit the inbox, not the spam folder.

Email Spam Filters

The ISP filter checks for the major sources of Spam and reject offending messages. These often handle the 75% of work for anti-spam operations. This includes checking for Email Relays, IP Reputation, Authentication (Phishing), botnets and simply accepts or denies a senders from proceeding to send their email. When mail is rejected here, a bounce is sent to the sender for later handling. (Infusionsoft automatically handles these for you.)

The Content Filter rests between the email recipient and their ISP. These handle about 20% of anti-spam operations. This will often check the email for content that doesn’t meet their standards, such as malicious attachments, spammy words and even the overall "fingerprint" of the email itself. When mail is rejected here, it’s silent and often the user doesn’t know. Some ISPs may bounce the message back with details, but not always.

Finally, the Personal Filter is the filter that happens when the recipient’s email software filters the messages on its criteria. These handle about 5% of anti-spam operations. Depending on the email service, the ISP may offer this through a web-based interface or in the case of Outlook, it’s running with the email client. These filters honor any request by the recipient. When mail is rejected here, it’s silent and often the user doesn’t know until they specifically look for the message. (Don’t believe me? Try syncing your Gmail account in Outlook and watch what lands in the "Junk Email" sub-folder. It’s a pretty liberal spam filter.)

What do you do with this information? That, I can’t tell you. It’s up to you.

Infusionsoft (along with any reputable ESP) has a good IP reputation and a Feedback Loop (FBL) established with ISPs so they can handle any complaints that come through. Infusionsoft also makes it easy to build standards-compliant emails, so that’s covered. We recommend users adhere to industry-leading best practices so you don’t get flagged as a spammer. Lastly, we drop spammers when we encounter them, preserving good deliverability for all the rest of our users.

If there’s one nugget of advice to takeaway from all this, it’s this:

Encourage recipients to add your email address to their address book. This is known as Whitelisting and often Whitelists supersede Content Filters to your recipients email inboxes. With Infusionsoft, you can ask people to add your email address to their address book, and many people will if they want to continue receiving your messages.

Now for a little disclosure. I used to work within the AOL Postmaster team. During my tenure there, I learned a lot about how they (specifically AOL/AIM/Netscape/CompuServe) filter their inbound email. No information from this article is proprietary or confidential — at least I hope not. AOL sets the standard when it comes to aggressive spam filtering, so I can only assume other top-tier ISPs follow suit.

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