Email deliverability glossary

0-9

250ok: A response sent from ESPs that indicates a message has been accepted. 250ok doesn't mean that the email was delivered to an inbox, only that the ESP did not reject the message.

A

Allow list: A custom rule that allows email traffic from a specific IP address, email address, or domain. Allow lists are usually set up to ensure that no wanted email messages are blocked. Typically, emails from your internal company team or critical alerts are added to allow lists.

Alt text: Alt text is supplementary text added to images in HTML, and is usually added to describe the contents of the image. If your image is blocked by a mail provider, the alt text remains visible. Also, some email filters look at the alt text of images in your emails as part of their filtering process.

Authentication: A general term used to describe the different ways in which ESPs and mailbox providers secure their email messages. Examples of email authentication include Sender Policy Framework (SPF) and Domain Key Identifier Mail (DKIM). For more, check out Email deliverability overview.

B

Brand Indicators for Message Identification (BIMI): This allows you to display your logo in subscriber inboxes. This can help your emails stand out and increase opens and other engagement metrics.

BIMI relies on DMARC policies and authentications to ensure that your domain isn't being impersonated. Keep in mind that not all mailbox providers support BIMI, and each provider has its own policies.

For more information about displaying your logo in subscriber inboxes, see Display your brand’s logo in subscriber inboxes. For more information about BIMI, visit https://bimigroup.org/.

Blocklist: Domain and/or IP-based lists of email senders that are known spammers or who have recently sent spam-like emails. Blocklists are operated independently and are used by mailbox providers around the world. See What's a blocklist? for more information.

Block: A blocked, soft bounce, is another type of email delivery failure. Usually, emails are blocked when subscriber email inboxes are full and can’t accept additional emails. Blocked emails are also used to indicate poor sender reputations or suspected spamming. You may also see the terms 4.x.x or 4xx to refer to blocked emails. 

Bounce: A bounce, or hard bounce, is one type of email delivery failure. Usually, emails bounce when subscriber email accounts are no longer active. You may also see the terms 5.x.x or 5xx to refer to bounced emails.

Bulked: See Spam folder.

C

Click: In email metrics reporting, a click is when a subscriber clicks on a URL or an image that includes a URL and the subscriber visits the corresponding page.

Click-through rate (CTR): The percentage of subscribers that both opened and clicked on a link in an email.

Content filter: An email technology that scans email content to determine if the message, or links within the message, are safe.

D

Dedicated IP: An IP address used by a single sender or single brand to send their email. When using a dedicated IP address, senders are solely responsible for the reputation of their IP.

Deferred: A 4xx SMTP error. When sent emails are deferred, Attentive will continue attempting to send the message for 72 hours. 

Deliverability: A holistic view of all of the factors that can impact whether or not an email is delivered. For more, check out Email deliverability overview.

Delivered: An email message that was accepted by the mailbox provider and was delivered to the inbox, a Gmail tab, or spam folder. Messages that are delivered return 250ok.

Domain Key Identified Mail (DKIM): Cryptographic authentication used to protect email messages during transmission.

Domain-based Message Authentication, Reporting, and Conformance (DMARC): This is a protocol that strengthens your domain’s existing authentication. A DMARC policy tells the receiver what to do if neither SPF nor DKIM passes authentication. For example, DMARC can specify that an email should be quarantined or rejected in those scenarios.

In conjunction with SPF and DKIM, DMARC helps stop spammers from impersonating your brand. It also offers the following benefits:

• Clear instructions for recipient email/server administrators about how to handle emails if they're flagged by SPF (e.g., quarantine or reject the email).
• A way for recipient email/server administrators to send feedback when an email fails authentication. This allows marketers to get crucial and immediate feedback about authentication issues.
• Ability for the sender to specify how reports and samples can be sent back for examination.
• Ability for recipient servers to send real-time feedback to the sender.

E

Email Service Provider (ESP): ESPs are message transfer agents (MTAs) that send email on behalf of customers. ESPs can be cloud-based or on premises, and usually offer tools to send email at large scale and analytics to understand the effectiveness of their email messages.

F

Feedback loop (FBL): Feedback loops are mechanisms used by mailbox providers to report user complaints back to the sender so that the email address can be suppressed from receiving future messages.

Freemail: Free email accounts provided by companies like Gmail, Outlook, and Yahoo.

I

Inbox rate: Percentage of email messages that were accepted by the mailbox provider and delivered to the inbox or another tab within the inbox.

Internet Service Provider (ISP): Sometimes referred to as mailbox or inbox providers, ISPs host email clients for their subscribers. ISP is commonly used to refer to companies like Google, Microsoft, Yahoo, and Comcast.

IP address: Internet Protocol address. IP addresses are unique addresses used to identify devices on the internet. A sender IP address is used to send email from mail servers to mailbox providers.

L

Local-part: The part of an email address before the @ symbol. For example, the local-part of the email address hello@attentivemobile.com is hello.

M

Mailbox Provider (MBP): Sometimes referred to as internet service providers or mailbox providers, are companies that host email clients for subscribers. MBP is commonly used to refer to companies like Google, Microsoft, Yahoo, and AOL.

O

Open: An email engagement metric indicating when an email you sent to a subscriber was opened. Email opens are tracked with a tracking pixel that when viewed by subscribers indicate that the email was opened.

P

Pre-text (or preview text): An HTML snippet that reinforced the subject line by providing additional context. Pre-text is visible in most email clients as additional text that appears below the subject line. In some mailbox providers like Gmail, the pre-text is only visible when viewing the inbox and doesn't appear when the email is opened.

Pristine: Pristine email addresses are email addresses that have never been published on the internet or otherwise circulated on the internet. Pristine email addresses are typically scraped from web forms, bought on auction sites, or traded on the dark web. Pristine email addresses are often used as part of a spam trap.

R

Recycled: Recycled email addresses were once valid, but have since been abandoned by the original owner. Recycled email addresses are usually identifiable by a lack of opens and clicks over time. Recycled emails are often used as part of a spam trap.

Role account: Email addresses that are accessible by multiple people within an organization who have a particular role. In general, you should avoid including role account email addresses in your list. Because email messages sent to role account addresses may be seen by many people, it increases the likelihood of the message being reported as spam. See What’s a role account? for more information.

Root domain: The domain name minus any periods. For example, the root domain of https://www.attentivemobile.com is attentivemobile.

S

Shared IP: An IP address shared by multiple organizations to send email. All senders on a shared IP address contribute to and share the reputation of the IP address.

Spam folder: A folder in an email inbox where messages suspected of being spam are sent. ESPs use domain reputation, previous poor practices, or sophisticated algorithms to help determine if a message is spam. If a subscriber marks a message as spam, it’s also sent to the spam folder. You don't want your message to land in the spam folder.

Spam trap: An email address abandoned by the original owner, one that contains a typo, or has never been circulated. Spam traps are monitored by blocklist operators to identify spammers or organizations with poor email list hygiene.

Sender Policy Framework (SPF): A text record that contains all of the IP addresses that are authorized to send email on behalf of the From domain.

Subject line: The first part of every email message that subscribers see and is visible both in the email inbox and after opening the email.

T

Typo: An email address that was mistyped at the point of collection. Typos occur frequently with mobile opt-in. For example, hello@attentivemobiler.com or @gmal.com.

U

Unique click: A tracking metric that looks at the first time each URL in an email is clicked. Each subsequent click is ignored.

Unique open: A tracking metric that looks at the first time an email is opened. Each subsequent open is ignored.