E-Mail Deliverability: The Challenges

For over a year, email deliverability has been top of mind for email marketers. It will remain a concern for some time.

Though the attention devoted to deliverability issues is well founded, certain challenges may have been overstated by ill-informed marketers and the media. As a result of corporate and ISP filters, blacklists, and constant email address flux, permission-based marketers face daunting obstacles in their attempt to deliver solicited, confirmed-consent messages to the inboxes of customers and subscribers with whom they’ve established relationships.

We believe delivery begins when a recipient grants permission to receive your messages. If your email marketing strategy is based on this premise, delivery challenges are minimized. With permission, the customer or recipient is also your ally and can provide recourse if an ISP, spam filter, or blacklist blocks your messages.

We intend to separate deliverability fact from fiction. We’ll examine current and future challenges and provide insight for both beginning and advanced marketers. Each column will tackle a specific deliverability issue and keep you informed of new developments, such as the emerging role of reputation services. We promise to provide practical tips and best practices.

So what is deliverability? With email, it’s simply the ability to deliver a message to a recipient’s inbox.

A number of factors hinder or prevent solicited email delivery:

  • ISP-blocked incoming mail. The most common version of ISP blocking. Many ISPs, especially large ones, maintain internal blacklists of IP addresses that are denied any incoming connections. Frequent customer complaints about traffic from particular sources are the most common cause of this kind of blocking. ISPs tend to block IP ranges without any notification, as they routinely handle complaints about hundreds of thousands of individual email sources.

  • ISP-blocked outgoing mail. Your ISP blocks outgoing traffic to another ISP. This is rare, as most ISPs block incoming traffic, but it has been known to happen.
  • Distributed content filters. Several anti-spam companies help ISPs and enterprise customers cope with the influx of unsolicited email. Brightmail and Postini are two leaders in this field. These blocking systems employ complex content analysis heuristics that scan message content and create message “signatures” that are disseminated among the filtering company’s client base.
  • Public list. Publicly accessible blacklists and whitelists, maintained by volunteers, are often used by smaller ISPs and companies without dedicated email administrators. The most widely used lists are Mail Abuse Prevention System (MAPS), SpamCop, Spamhaus, and Spam Prevention Early Warning System (SPE)WS. Listing criteria can be reliable or near capricious, depending on the list owner’s preferences. Administrators select the lists that most closely match their company’s policy.
  • ISP content filters. Similar to distributed content filters, ISPs often employ content filters created internally or adapted from others. Content filters scan for a variety of red flags. They can even learn new patterns in spam email, such as inserting periods in words that would normally trigger a block. SpamAssassin is a popular open-source content filter and one of the best examples of how these filters operate.
  • User content filters. Almost every email client provides junk mail filters. These vary widely in complexity. Microsoft Outlook’s filter simply searches for offensive keywords and key phrases, whereas more robust filters can be configured to run from a user’s desktop.
  • User lists. Recent upgrades to email applications, including AOL, MSN, Yahoo, and Outlook, allow users to compile their own black- and whitelists of individual and domain addresses. Challenge/response systems extend this process by requiring non-whitelisted senders to respond with a code or other confirmation before their messages are delivered.
  • Message bounces. A soft bounce is a temporary failure; the email wasn’t delivered but may be retried in the future. It may be because the mailbox was full or the receiving mail server didn’t respond. A hard bounce means the message is permanently undeliverable. Perhaps the address is invalid, or a remote server is blocking your server.

Are there specific questions or issues you’d like to see covered in future columns? Let us know.

Want more email marketing information? ClickZ E-Mail Reference is an archive of all our email columns, organized by topic.

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