You already know not to judge a book by its cover, but did you know the same applies to email? Thankfully we have spam filters to take care of that. Historically we’ve understood mailbox providers to base their filtering decisions on content and subject lines, but they quickly learned there’s more than meets the eye. To maintain trust for the sender, through the gateway, and from the customer, mailbox providers must ensure that only legitimate, wanted mail makes it to the inbox.
Today’s spam filters take a wide approach in deciding the legitimacy of mail. While content still holds weight, reputation and infrastructure are the backbone to your representation as a sender. Whether a homebuilt system used by Gmail, or third-party technology used by a small email provider, spam filters continue to develop sophisticated, real-time algorithms to learn who you are as a sender, what you’re sending, and how it compares to other mail coming through the filter.
Reputation
IP address reputation is key in determining mailbox placement. Based on reputation drivers such as complaints, spam trap data, volume patterns, and blacklists, reputation-based filters will generate a score between 0 and 100 to decide your credibility as a sender. This gives the mailbox provider insight into all activity coming off of your IP address, not just the message you’re sending to their gateway. Regardless of your message’s validity, if other spammy behavior is detected from the sending IP address during the time of deployment, chances are your message will be filtered for another’s wrong-doing. It’s important to monitor all activity coming off of your sending IP address to ensure wanted mail is making it to the inbox.
Infrastructure
In order for a mailbox provider to trust the relation between incoming messages and its physical origin, all mail must meet infrastructure standards. This means authenticating with SPF, DKIM, and DMARC, and ensuring the hostname identifies with the sending server, therefore declaring the sender is who they say they are. A proper infrastructure will keep spammers from identifying with legitimate mail servers through unauthorized IP addresses or domains. This not only protects the end-user from dangerous phishing attacks, but can also alert the sender of a potential server risk.
Content
Once it’s established that you’re a good, legitimate sender, spam filters will compare the body and subject of your email against other mail deemed “spammy” or “legitimate” seen within their network. While the general understanding of spam comes into play with trigger words like “Viagra” or blacklisted link shorteners, what appears to be legitimate content could easily be classified as spam in light of real-time feedback. Content testing may reduce your chance of sending spam-like emails, but by maintaining a good reputation and exercising email best practices in conjunction with sending what you believe to be legitimate mail, the likelihood of placing to the inbox increases immeasurably.
Curious to learn more about spam? Check out Return Path’s new ebook, The Ultimate Guide To Email Deliverability.