You invest so much time and effort into creating emails that drive brand awareness, engage subscribers, and encourage your audience to take action and convert. But if your email never hits the inbox, all that hard work can be for nothing.
While email deliverability can be a bit of a mystery, understanding some of the more technical terms that play into it can make it a little less daunting. If you’re looking for how to fix your email deliverability, you get stuck on all the acronyms to keep track of: DMARC, DKIM, SPF…what does it all mean?
To help, we’ve created this cheat sheet of 33 email deliverability terms that you can keep on hand for easy reference. Print one of these out and stick it right above your desk—so you’ll never mix up soft bounces and hard bounces again.
If you’re stumped on a certain term, click a link below to take you straight to it and related terms:
- What is email deliverability?
- Sender reputation and authentication
- Email performance and subscriber behavior
- List management and hygiene
- Email deliverability FAQs
Otherwise, study up—this is your comprehensive guide to email deliverability terms:
What is email deliverability?
Email deliverability is a measure of whether or not the email messages you send make it to your subscriber’s inbox rather than the spam folder. Deliverability refers to inbox placement. Does the message go to a folder like Gmail’s Promotional Tab, the primary inbox, or to spam?
Email deliverability is different from email delivery, which refers to whether or not a receiver (mailbox provider) accepts the message you’ve sent. You can have great email delivery (all of your emails arrive in a subscriber’s mailbox) but poor deliverability (and they all landed in the spam folder, womp womp.)
Several factors influence your deliverability, starting with your sender reputation and authentication.
Sender reputation and authentication
Investing in your email-sending infrastructure helps build a better sender reputation, which boosts your credibility when sending emails. That includes:
IP Reputation
Internet Protocol (IP) addresses uniquely identify you and your server. Every computer has one, including the one (or the smartphone) you’re reading this blog post on right now.
Your IP reputation is attributed to an IP address based on what metrics an inbox service provider (ISP) has historically seen from that IP address and how users engage with mail that originates from it.
Domain Reputation
Your domain refers 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.
Because email isn’t always sent from just one IP address or provider, ISPs also use your sending domain to track reputation. That allows a receiver to accumulate a reputation score across the board.
Sender Policy Framework (SPF)
SPF (pronounced /ˌes.piːˈef/) 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.
DomainKeys Identified Mail (DKIM)
DKIM (pronounced /ˈdiːˌkɪm/) allows your organization to claim responsibility for your email. 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, and Conformance (DMARC)
DMARC (pronounced /ˈdiːˈmärk/) 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.
Brand Indicators for Message Identification (BIMI)
BIMI (pronounced /ˈbi.mi/) is a text record that is used to verify information about your brand that works right alongside SPF, DMARC, and DKIM. It signals to email clients that you are you. What makes BIMI extra interesting for email marketers is that verifying with BIMI can unlock brand imagery in the inbox and/or a blue verified checkmark, depending on the email client, which adds credibility to your messages and can (theoretically) increase your open rates.
DNS Record
The domain name system (DNS) is a naming database where your domain name is located and translated into an IP address. Basically, it’s where all of your authentication protocols live.
MX (Mail Exchange) Records
A DNS Mail Exchange (MX) record tells mail servers where to direct an email message in accordance with the Simple Mail Transfer Protocol (SMTP). This is the back-end magic that connects your message to the right email address. Failure to configure your MX record correctly could result in a higher bounce rate or delivery issues, which in turn impact your deliverability.
IP Warming
IP warming is the process of slowly increasing the volume of email you send from a new domain or IP address. Whether you’re switching to a new email service provider (ESP), getting started sending emails for the first time, or going through a merger or acquisition, IP warming can help maintain your deliverability.
This gives ISPs time to evaluate your authentication protocols, content, and infrastructure to determine that you’re a legitimate sender. As you establish your sender reputation, you can ramp up to your normal send volume.
DNS Pointer Record (PTR Record)
DNS PTR Records help you match IP addresses to sender domain names. When you run a reverse DNS lookup with your IP address, the PTR record finds the domain name. (This is the opposite of an “A” record, which gives you the IP addresses associated with a given domain name.)
Greylisting
Greylisting is an email security practice mail servers use to protect their users from senders they haven’t received mail from before. Rather than completely block your message, your email will be temporarily rejected.
The logic is that if the mail is legitimate, the originating server will try again to deliver the message after a delay, at which time the email will be accepted. A spammer wouldn’t take the time to retry sending an email as they’re going through thousands of email addresses.
Email Sender Reputation
All of this adds up to your email sender reputation, which is a score that ISPs assign to an organization that sends emails. ISPs evaluate your sender behavior (the volume of emails you send, and how often you send them), your infrastructure (the authentication measures you take to keep your subscribers safe), and your subscriber behavior (your email marketing performance and subscriber engagement) to determine your sender reputation.
The better your reputation, the more likely you’ll have a higher email deliverability score.
Ensure your emails reach the inbox
Understand the factors affecting email deliverability. Implement best practices to make sure your emails reach your subscribers.
Email performance and subscriber behavior
Setting up your authentication infrastructure is a must-do for your deliverability because it’s directly tied to email performance and how subscribers respond to your emails. Mailbox providers want to see that subscribers open, read, and engage with your emails. Here’s what you should look for:
Open Rate
Open rate is usually the first metric that email marketers look at to determine the success of their email campaigns. Open rate measures how many of your delivered emails were opened. While this can be a useful indicator of your subject line and preview text performance, changes like Apple’s Mail Privacy Protection (MPP) make open rates a less reliable success metric.
Click-Through Rate (CTR)
Your click-through rate (CTR) determines how many clicks your emails received. You can calculate click-through rate by dividing the number of emails clicked by the number of emails delivered. Taking opens out of the equation gives you a more accurate picture of email engagement.
This is often confused with click-to-open rate (CTOR), which measures how many of your opened emails received clicks. This is a better indicator of how your subject line and preview text perform, versus your overall engagement.
Rendering Issues
Rendering issues occur when email clients change the display of how your email appears—Outlook, we’re looking at you—that make it difficult or impossible to interact with. While rendering issues happen to the best of us, they can make your email campaigns look a little spammy to ISPs. (And depending on how wonky things get, your subscriber won’t be able to engage much with your email, either, which doesn’t help your deliverability.) That’s why we always recommend testing your email before you send it.
User Engagement
Engagement refers to how your subscribers view and interact with your emails. Think of your user engagement metrics as that sweet spot in the middle of the funnel, which includes open rate, click rate, and read time. ISPs look at your user engagement to determine your inbox placement—the more your subscribers interact with your emails, the better your deliverability will be.
Unsubscribe Rate
Unsubscribe rate measures how many people opt-out of your emails. Depending on your email platform, an “unsubscribe” could be if someone actually opts out or if they click your unsubscribe link but don’t follow through. New deliverability guidelines from Yahoo and Gmail require one-click unsubscribes and that you process these requests in 48 hours or less.
Feedback Loop (FBL)
Feedback loops allow the sender to receive a report every time a recipient clicks on the “mark as spam” or “junk” button. Subscribing to feedback loops and using this data to quickly remove folks who are no longer interested in your email helps maintain a positive reputation.
Spam Complaints
A spam complaint is when a recipient marks your email as spam. This is an example of negative engagement—you’re probably not a spammer, but for whatever reason, your subscriber doesn’t want to see your emails anymore. This is why it’s so important to make it easy for subscribers to unsubscribe. While no one likes a high unsubscribe rate, a high spam complaint is much worse for your overall deliverability. To comply with Gmail and Yahoo’s new deliverability rules, you should keep your spam complaints to less than 0.3%.
Bounce Rate
The email bounce rate is how many of your sent emails weren’t delivered. This can be for temporary reasons like a too-full inbox (soft bounces) or permanent reasons like an incorrect email address (hard bounces). A high bounce rate is a sign of poor list hygiene or a problem with your acquisition practices. If you’re seeing a bounce rate above 2%, address this problem asap as it has a big impact on your email deliverability. There are two types of bounces:
Soft Bounce
When an email bounces, it means that it never makes it to your subscriber’s mailbox. (In other words, it’s a delivery issue, not just a deliverability issue.) 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. When a soft bounce happens, keep an eye on that email address—you don’t have to do anything yet, but if it keeps bouncing, you may need to clean it from your email list.
Hard Bounce
Unlike soft bounces, hard bounces require immediate action. 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. A hard bounce indicates a permanent reason that an email can’t be delivered, so you should remove them from your email list.
Inbox Placement Rate (IPR)
Inbox placement rate shows the percentage of emails that get delivered to a subscriber’s primary inbox, rather than the spam folder or other folders like Gmail’s Promotions Tab.
It’s important to track all of these metrics when thinking about your deliverability. But if you were going to pick one to focus on, it’s your inbox placement rate (IPR). These are just a snapshot of the metrics you should evaluate for your email marketing strategy. Check out our full list of email marketing metrics to help you measure the impact of your emails.
Spam folder no-more
Implement best practices to keep your emails out of the spam folder. Improve your deliverability rates and reach more inboxes.
List management and hygiene
Deliverability starts with your email list. Email marketers must balance acquisition pressure—the goal shouldn’t be to grow your email list with just any email addresses you can find, but rather build an audience of subscribers that care about what you have to say. Here are a few terms you need to know as you go through your email list management:
List Hygiene
List hygiene, or list management, is the practice of maintaining an email list of subscribers that actually want to hear from you. Proper list hygiene requires regular checks of your email list for typos, outdated email addresses, or subscribers who have stopped engaging with your emails altogether.
Opt-In
An opt-in is another way of saying that someone has subscribed to your list. The right opt-in practices can prevent list hygiene issues in the first place—like watching for common typos like “gmial” instead of “gmail.” There are two kinds of opt-in practices, single opt-in and double opt-in:
Single Opt-In
Single opt-in (SOI) is when someone subscribes to your mailing list without confirming their email address. Once they type in their email address and click “subscribe,” they’re in. This is a popular acquisition method because it reduces the number of steps subscribers have to take to sign up, but it can make it more difficult to catch typos, bounced email addresses, or spam traps.
Double Opt-In
Double opt-in (DOI), also known as confirmed opt-in (COI), is when someone subscribes to your mailing list and then must confirm their email address in a two-step process. First, someone types in their email address and clicks “subscribe” on an opt-in form or checkbox. This triggers a confirmation email where the would-be subscriber must click “confirm” to be added to your email list. While it adds another step, a double opt-in can help with spam complaints and data privacy compliance.
Spam Traps
Spam traps are commonly used by inbox providers and blocklist providers to catch malicious senders. They are email addresses that were once used by real people, but due to inactivity, have been reclaimed by the ISP to identify spammers. (But, legitimate senders with poor data hygiene or acquisition practices can end up with spam traps on their list). Its only purpose is to identify spammers and senders not utilizing proper list hygiene. This is one of the big deliverability reasons not to purchase an email list.
Opt-Out
Opt-out is another word for unsubscribing, or when someone requests to no longer receive your emails. (See unsubscribe rate, above.)
Spam Folder
The spam folder, also known as the “junk” folder or spam filter, is designed by ISPs to filter out suspicious emails. This includes dangerous or well-known scams, inappropriate or illegal content, or phishing attempts, which compromise the safety and security for the ISP’s users. Spam filtering has become so sophisticated that sometimes email marketers can get caught, too. If you’re consistently landing in the spam folder, you need to evaluate your email marketing strategy.
Blocklist
You don’t want to end up on a blocklist (formerly known as blacklists). A blocklist is a list of IP addresses or domains that are known to be associated with malicious spammers.
There are two kinds of blocklists:
- IP blocklisting indicates to anyone who utilizes that blocklist to block the mail originating from that IP address.
- More serious is domain blocklisting. Email marketers can send campaigns from multiple IP addresses, but if your domain appears frequently in emails that hit spam traps, there may be a chance that your entire domain will be blocklisted. 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.
On a practical level, individuals can create their own blocklists of senders that are not allowed to email them for whatever reason—a step beyond a spam complaint, if you will.
Allowlist
Allowlist, previously known as a whitelist, is the opposite of a blocklist. Your subscribers can save you from the spam filter by explicitly telling their mailbox provider that they want to receive your messages. Depending on the inbox provider, they can go into their settings and mark your messages as TINS (This Is Not Spam). This means your server is considered spam-free or is an “approved sender.”
Email Throttling
ISPs can detect a change in email volume, so if you start sending too many emails too quickly, you risk having some (or all) of your emails rejected. Email throttling is when an ISP limits the amount of emails accepted from a sender during a certain time period. When this happens, you’ll see a large number of email bounces. This can also happen if you’re seeing an uptick in spam complaints or unsubscribes—basically, the ISP is wary of your sender reputation and wants to slow it down in case you are a spammer. (Even if you’re not!)
Email deliverability FAQs
Still have email deliverability questions? We’ve compiled some of the questions our customer support team gets most often:
What factors affect email deliverability?
Several factors affect your email deliverability:
- Email volume: ISPs look at the number of emails you send, and how frequently you send them, to determine if you’re a spammer.
- Authentication infrastructure: You should have your t’s crossed and i’s dotted with your authentication, including SPF, DKIM, and DMARC.
- List quality and engagement: How often, and how well, your subscribers engage with your list matters for your deliverability. This is often informed by your list management—whether or not the email addresses on your list want to hear from you in the first place.
- Email content and formatting: Make sure your emails look good in mobile, Dark Mode, and on all email clients before you send. While the impact of your email content is lower than the other factors here, it’s still important as it affects your engagement, which in turn affects your deliverability.
All of these add up to your sender reputation, which is the score ISPs look at when determining your inbox placement.
Why are my emails going to the spam folder?
After analyzing thousands of emails, we found that 70% of emails show at least one spam-related issue, so it’s important to look at your email marketing program holistically for deliverability fixes.
There are a few things you can do if you’re seeing a large percentage of emails going to the spam folder:
- Check your authentication and infrastructure: Make sure everything is working correctly with your authentication protocols like SPF, DKIM, and DMARC. Then, double check your infrastructure like your IP reputation.
- Check your spam complaints: If someone marks you as spam, you’re going to end up in the spam filter. If you’re seeing a lot of spam complaints, it may be a mismatch between your audience and your content, or your send frequency.
- Check your unsubscribe process: Frustrated people trying to unsubscribe from your list may resort to spam complaints. Is it easy for them to unsubscribe? And double check that you’re honoring those unsubscribe requests as soon as possible.
Here are a few more ways you can improve your deliverability.
How do you fix email deliverability?
Fixing your email deliverability depends on what caused the problem in the first place—ah, the fickle nature of email!—but there are a few best practices you can follow to address deliverability issues:
- Regularly clean your email list: Email list hygiene is not a one-and-done process. One of the first checks you should make (after your infrastructure setup) is your email list. Look for email addresses that have typos, have recently bounced, or no longer engage with your emails.
- Use email personalization to boost engagement: High engagement is the secret to better deliverability. Prove to ISPs that your subscribers love getting your emails and you’re more likely to land in the inbox in the future. Segmentation and personalization are two techniques to achieve this.
- Switch to double opt-in: If you’re consistently struggling with your deliverability, it’s best to prevent issues at acquisition with a double opt-in process. This requires any new email addresses added to your list to be confirmed by a real person, so you know they’re legit (and that they actually want to hear from you.)
Here are a few more ways you can fix your deliverability.
What is a good deliverability rate for email?
A good email deliverability rate is 95% or higher. (Tbh, we aim for 99%.) That means 95% of the emails you send get delivered and placed in the inbox or another primary folder.
Don’t mix up deliverability rate with your delivery rate. That measures how many emails you send get delivered, period. While it’s important to have a high delivery rate as well (your emails can’t get placed in the inbox if they’re not delivered), make sure you’re looking at both when evaluating your email marketing performance.
How often should I clean my email list?
You should clean your email list regularly—at least every six months, if not every quarter. It’s a good idea to do a list audit after big email address acquisition events, too, like after a conference or partner marketing swap. Keep an eye on your unsubscribes and bounce rate on a regular basis, which are leading indicators of your overall list hygiene.
What role does email testing play in email deliverability?
ISPs evaluate a number of factors to determine whether or not your email should be placed in the spam folder or the inbox. If your emails look suspicious—they contain rendering issues, broken or hidden links, or weird formatting—you may get stuck in the spam filter. The best way to prevent this? Testing your email before every send. (We can help with that.)
What tools can help me monitor email deliverability?
When we asked email geeks about their deliverability practices, 22% admitted to not measuring deliverability at all. This shocked us because there are free tools like Google Postmaster out there to help you out. You can also use an all-in-one tool like Litmus Spam Testing, which looks at your overall deliverability health and evaluates specific email campaigns for spam filter flags.
Don’t let all these deliverability terms scare you
Phew, that was a lot! Deliverability is one of the trickiest parts of email marketing to master. But the good news is, you don’t have to memorize all of these terms right now.You can download our handy-dandy cheat sheet—or let Litmus do all the hard work for you. Litmus Spam Testing runs your email marketing campaigns through 20+ filters and provides actionable advice on how to improve your deliverability.
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This article originally published on May 18, 2016. It was updated on December 13, 2024.
The post A Comprehensive Glossary of Email Deliverability Terms appeared first on Litmus.
