28 Deliverability Terms Every Email Marketer Should Know


BY  KAYLA LEWKOWICZ Spam. No, we’re not talking about the gelatinous mass sometimes referred to as “dinner.”


Spam. No, we’re not talking about the gelatinous mass sometimes referred to as “dinner.”

As email marketers, we strive to produce great content and work to build emails that drive brand awareness, engage our customers, and encourage prospects to purchase our products. It sends a shudder down our spine to think about landing not in our subscriber’s inbox, but in the dreaded spam folder. It’s our duty to build something great, not spammy.
Yet deliverability is a tricky thing to master, in part because there’s a lot of technical language to learn. Here are 28 deliverability terms you need to know as an email marketer:


Let’s start with the basics. What are we even talking about? Often, marketers use delivery and deliverability interchangeably, but they mean slightly different things.
  • Delivery refers to whether or not a receiver accepts the message you’ve sent. Does the domain or email address exist, or is your IP address blocked or not? So if an email is successfully delivered, that just means that it made it to the intended recipient’s inbox or spam folder.
  • Deliverability or Inbox Placement refers to where that message ends up once it is accepted. Did it get to the inbox?
Imagine that every email you send is a traveler flying from a major airport. Successful delivery would mean that the traveler arrived at the correct airport, proved their identity (authentication) with a ticket and passport, and TSA verified them as safe to pass through security into the main terminal.
Once they cross through airport security, deliverability would be where their flight ultimately arrived. Most of the time, they can safely get to the departure gate (delivery) but then might be rerouted from Dallas to Houston because of weather (deliverability).
Similarly, there’s some confusion between the terms ESP and ISP:
  • ESPs, or Email Service Providers, provide platforms to send commercial and transactional email on your behalf. MailChimp, Pardot, Emma, Constant Contact (the list could go on an on!) are all ESPs.
  • ISPs, or Internet Service Providers, provide mailboxes to end users as part of their paid services. These are generally your cable or internet providers, such as Comcast and Verizon.
  • Inbox Providers include ISP-provided inboxes as well as paid or free webmail accounts and email apps. Examples of this would be Gmail, Outlook.com, Yahoo, or Inbox by Gmail.
Now, some internet-related basics:
  • IP Address: A number that uniquely identifies any device connected to the internet. “IP” stands for “Internet Protocol.” Similar to how a street address helps people find buildings, an IP Address helps computers find each other on the internet.
  • Domain: Similar to an IP Address, domain names refer to locations of servers and devices connected to the internet. Domain names can represent a whole bunch of different IP addresses. For example, the domain www.litmus.com would address the collection of servers that host our website. Whether that is www.litmus.com/blog or www.litmus.com/community, the domain is the same.
  • Sub-domain: In our case, litmus.com is our domain name. Email.litmus.com is a sub-domain of litmus.com that we use for marketing emails. Subdomains are useful, as they can be used to isolate mail streams from one another for both branding and reputation reasons.


Investing in your email-sending infrastructure helps build a better sender reputation, which boosts your credibility when sending emails. Your sender reputation is essentially a score, like your credit score, that immediately signals how trustworthy you are to an ISP. Each organization and ISP might have different scores for you.
There are two types of sender reputation:
  • IP Reputation: IP addresses uniquely identify you and your server (see above). Reputation is attributed to an IP address based on what metrics an ISP has historically seen from that IP address and how users engage with mail that originates from it.
  • Domain Reputation: This has become more important in recent years. Email isn’t always sent from just one IP address or provider, so using your sending domain to track reputation allows a receiver to accumulate a reputation score across the board. That means taking ownership over your sending domains is imperative to the the health of your entire organization and brand reputation.
This SendGrid article talks more about the different types of sender reputation. You need both a good IP reputation and a good domain reputation to effectively deliver your email.
Other aspects of sender reputation include:
  • Domain Name System (DNS): This is a way of resolving a domain name into an IP address. It’s basically like a telephone book that keeps track of everything.
  • MX, or Mail Exchange, DNS Record: This is a specific type of DNS record specifying where mail that is destined for a domain name should be sent. It denotes the host responsible for receiving mail, not the sender. Essentially, it’s the server that mail for that domain is sent to.
  • TXT DNS Record: A place to store extra information about the domain, often arbitrary text or binary data. TXT records may be used for authentication purposes.
  • Uniform Resource Identifier (URI): A domain plus more information about what we want from that server. When we think of a URL, it’s actually a type of URI identifying a resource by its primary access point (it’s “location” on the web).
Get your email scanned by every major spam filter before you send with Litmus’ Spam Filter Testing.


Just as travelers show their passports and plane tickets, emails must pass through authentication to prove that an email is from who it says it’s from. Here are a few terms you’ll want to familiarize yourself with:
  • Sender Policy Framework (SPF): A sender policy framework allows mail services to double check that incoming mail from a specific domain has, in fact, been sent from that domain. SPF protects the envelope sender address, or return path, by comparing the sending mail server’s IP address to a master list of authorized sending IP addresses as part of the DNS Record (see above).
  • DomainKeys Identified Mail (DKIM): This allows your organization to claim responsibility for your email, the same way a minor needs to be claimed by parents or guardians when travelling internationally. It’s an identifier that shows your email is associated with your domain and uses cryptographic techniques to make sure it should be there.
  • Domain-Based Message Authentication, Reporting, & Conformance (DMARC): Designed to combat phishing, DMARC gives you insight into the abusive senders that may be impersonating you–and can help you identify them. It allows a sender to indicate that an email is protected by SPF or DKIM. The sender can then receive a report back on any messages that failed the authentication and identify if anyone using the domain could be a spammer.


It can be difficult to track how you’re doing. Spam filters, designed to keep spam out of the inbox, can sometimes pick up any marketing content. Using Litmus’ spam filter testing can help determine whether or not you’ll be marked as spam, but several other factors must also be taken into account:


  • Hard Bounce: Hard bounces occur when the receiving server is either unable to deliver or rejects the message. It can also occur when there is no mail server at that address, or the domain doesn’t exist at all. This can be caused by anything from typos to deleted user accounts. In most cases, if you receive a hard bounce, immediately removing them from your list is the best course of action. A hard bounce indicates a permanent reason that an email can’t be delivered and that this address should not be mailed to in the future. Removing them doesn’t necessarily mean deleting them; you can also deactivate them or add them to a suppression list. That way, you won’t re-acquire the same invalid email address and send to it again.
  • Soft Bounce: A soft bounce means that the recipient exists, but for whatever reason, they couldn’t receive your message. Soft bounces typically indicate temporary delivery issues. This could mean a user’s mailbox is full. Though this isn’t your fault, you should eventually consider them to be the same as hard bounces. MailChimp, for instance, unsubscribes users that soft-bounce seven times in a row. It could also mean the email you sent exceeded the maximum size the subscriber’s inbox allows. In addition, Rate-Limiting or Throttling might be at play. If you send large volumes of email to the same ISP, you might start being throttled. An ISP may only allow a certain amount of connections per hour or per day, so if you exceed that, you may get blocked.


Different subscriber behaviors can change your deliverability and affect your sender reputation.
  • Spam complaints: This is when your recipient marks your email as spam. It could be the recipient felt you didn’t have permission to email them, you were emailing too frequently, or were sending irrelevant content. As Litmus Research Director Chad White says in his book, Email Marketing Rules, “Having permission only gets you so far nowadays. Irrelevant and unwanted email is the new spam in the eyes of both consumers and Internet Service Providers (ISPs).” Keep in mind that the way your customers define spam may differ from the technical definition.
  • Feedback loops: A feedback loop allows the sender to receive a report every time a recipient clicks on the “mark as spam” or “junk” button. To maintain a clean email list, you can then suppress, or prevent, unwanted messages from appearing in that particular inbox. Subscribing to feedback loops and using this data to quickly remove folks who are no longer interested in your email helps to maintain a positive reputation. For more on feedback loops, check out this great guide from SparkPost.
  • TINS (This Is Not Spam): By marking something as NOT spam, your subscribers may save you from the spam filter. This requires them to go into their spam folder and manually whitelist your address.
  • Whitelist, or whitelisting: The opposite of a blacklist, this means your server is considered spam-free or is an “approved sender.” It’s often used by email applications to allow users to mark whether or not they trust emails from specific senders, this overrides some of the filtering that may exist from the ISP. You can also apply for whitelisting programs that a few ISPs offer. (Going back to our airport analogy, this is like TSA precheck). While not a guarantee to end up in the inbox, a sender may receive preferred delivery as long as they stay within the proper thresholds of the program.


It’s a marketer’s worst nightmare! Practicing good email list hygiene, or the practice of going through and cleaning up your subscriber lists, will help you sleep better at night. Here are some terms you may encounter that will prompt you to start scrubbing:
  • Spam Traps: Spam traps are commonly used by inbox providers and blacklist providers to catch malicious senders, but quite often, legitimate senders with poor data hygiene or acquisition practices end up on the radar as well. A spam trap looks like a real email address, but it doesn’t belong to a real person nor is it used for any kind of communication. Its only purpose is to identify spammers and senders not utilizing proper list hygiene. For more information, take a look at this post on how to identify spam traps and what to do about them.
  • Blacklist, or blacklisted: Over 500 nonpartisan organizations work to monitor and block web addresses that produce spam. Getting blacklisted is an email marketer’s worst nightmare! There’s a few different types of blacklisting that can occur:
  • IP Blacklisting: When you send an email, it will originate from an IP address. When an IP is blacklisted this indicates to anyone who utilizes that blacklist to block the mail originating from that IP address.
  • Domain blacklisting: If your domain appears frequently in emails that hit spam traps, there may be a chance that your entire domain will be blacklisted. This can be even more damaging as the block is not localized to just an IP address, thus affecting you across all your sending platforms. This is why it is important to use a separate subdomain for your email marketing.
In general, ISPs take engagement very seriously. If your email generates positive interaction and engagement it can boost your sender reputation. That means your standard success metrics, like opens and clicks, still matter. On the flip side, if your emails are consistently deleted without being opened or they are marked as spam, that doesn’t look good–for you as a marketer or for your deliverability.



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#DIGITAL: 28 Deliverability Terms Every Email Marketer Should Know
28 Deliverability Terms Every Email Marketer Should Know
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