Email Deliverability, in Plain English

Being an email marketer requires quite a vocabulary. MBP, IPR, filters, bounces, traps, reputation … huh? These are just a few of the many terms associated with email deliverability. It can be daunting to understand the alphabet soup of the industry, especially if you're relatively new to email marketing, much less know how to read and interpret various metrics.

Let’s break down these terms one by one:

• MBP: This acronym stands for mailbox provider, which refers to any company that provides end users (i.e., subscribers) with an email account. The largest MBPs in North America are Gmail, Yahoo, Microsoft, AOL, and Comcast.
• Filters: Every MBP handles large volumes of incoming email messages each day — sometimes in the billions. With that kind of volume, it can be tough to distinguish legitimate senders from spammers, so each MBP has a different process for analyzing incoming mail and determining whether the message is valid. These processes, called filters, are automated and highly dynamic, applied in real time as email flows through the MBP’s servers.
• Bounces: A bounce means that the message cannot be accepted by the MBP and is the email equivalent of “return to sender.” There are two types of bounces: hard and soft. Hard bounces indicate an email address is invalid or no longer exists; soft bounces indicate a temporary reason, such as a full inbox, for returning the message.
• Delivered rate: This is the ratio of your email that's making it through the MBP filter. Another way to define this metric is “net sent” (total email sent minus hard bounces). This means the MBP has accepted the message for delivery and hasn't rejected it because the mailbox doesn’t exist or any other reason. However, this metric doesn't indicate where messages are being delivered … more on that later.
• Blocked: This is the opposite of delivered. If email is blocked, the MBP filter has determined the message or sender is suspicious and has stopped the mail (and any other volume from the sender) from going through to the recipient.
• IPR: Not to be confused with delivered rate, this acronym stands for inbox placement rate. Once a message passes successfully through the MBP filter, it can either arrive in a subscriber’s inbox or their junk/spam folder. IPR refers to the amount of your email that successfully arrives in the inbox. On average, less than 80 percent of commercial email actually reaches the inbox.
• Traps (or spam traps): These are email addresses that aren't actively used by subscribers. There are two types of traps: pristine and recycled. Pristine traps are email addresses that were set up for the sole purpose of catching bad mailers and were never occupied by an active subscriber. Recycled traps were once active email accounts that have been abandoned by their subscribers and lain dormant for a long period of time. If a sender has a lot of traps in their mailing list, it can cause email to be blocked by MBPs.

Unfortunately, running a successful email program isn’t it as easy as clicking the “send” button. There are a number of potential pitfalls for a message from the time it leaves your email platform to the time it arrives in the subscriber’s inbox. You may not be able to avoid all of them, but having a clearer understanding of common terms is a good place to start in navigating the complex deliverability ecosystem.

For more details on these and many other important deliverability concepts, check out our Ultimate Guide to Email Deliverability.

Bonnie Malone leads the consulting, client training, and knowledge and editorial organization of Return Path, an email data solutions provider.