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.
To help, we’ve created these cheat sheets of 33 email deliverability terms that you can keep on hand for easy reference.
Here’s a preview of some terms we cover in them.
Email deliverability basics
- Delivery refers to whether or not a receiver (mailbox provider) accepts the message you’ve sent.
- Deliverability refers to where that message ends up once it is accepted.
- Email service providers (ESPs) provide platforms to send commercial and transactional email on your behalf.
- Internet service providers (ISPs) provide mailboxes to end users as part of their paid services.
- Inbox providers include ISP-provided inboxes as well as paid or free webmail accounts and email apps.
- IP address: Helps computers find each other on the internet.
- 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.
- Sub-domain: A sub-domain of the domain that can be used for needs like marketing emails, to isolate mail streams from one another for both branding and reputation reasons.
Sender reputation, authentication and infrastructure
Investing in your email-sending infrastructure helps build a better sender reputation, which boosts your credibility when sending emails.
- IP Reputation: IP addresses uniquely identify you and your server. 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: 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.
(Hint: You need a good IP reputation and a good domain reputation).
- Sender Policy Framework (SPF): 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): 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, & Conformance (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.
- Brand Indicators for Message Identification (BIMI). A text record that is used to verify information about your brand that works right alongside SPF, DMARC & DKIM and signal to email clients that you are you.
- 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. A hard bounce indicates a permanent reason that an email can’t be delivered.
- 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.
- Spam Traps: Spam traps are commonly used by inbox providers and blocklist providers to catch malicious senders. (But, legitimate senders with poor data hygiene or acquisition practices can end up on the radar). Its only purpose is to identify spammers and senders not utilizing proper list hygiene.
- IP Blocklisting: When you send an email, it will originate from an IP address. When an IP is blocklisted, it indicates to anyone who utilizes that blocklist to block the mail originating from that IP address.
- Domain Blocklisting: 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.
Different subscriber behaviors can change your email deliverability and affect your sender reputation.
- Spam complaints: Your recipient marks your email as spam. (And why it’s so important to let subscribers who wish, to easily unsubscribe).
- Feedback loops: Allows 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.
- TINS (This Is Not Spam): Subscribers may save you from the spam filter if they go into it and “allowlist” your address.
- Allowlist: The opposite of a blocklist, this means your server is considered spam-free or is an “approved sender.”
In general, ISPs take engagement very seriously. Focus on ways to engage your email subscribers so you consistently generate positive interaction.
Download your email deliverability cheat sheets now for a handy reference of key terms, whenever you need it. If you’re hungry for more, check out our Ultimate Guide to Email Deliverability.
This article originally published on May 18, 2016. It was updated on October 21, 2022.