Email glossary
Email terms, explained.
Short definitions for the words you run into when you set up sending, fix deliverability, or dig through docs. From SPF and DKIM to bounces, reputation, and webhooks.
B
BIMI
Shows your brand logo next to messages in some inboxes when authentication passes.
Blocklist
A public list of IPs or domains that receivers treat as risky or refuse to accept.
Bounce
The receiving server rejected the message, so it never landed in the inbox.
Bounce Rate
The percentage of emails that failed to deliver in a given period.
C
Catch-all
A domain setting that accepts mail for any local address, even ones that are not real users.
Click-through Rate
The percentage of recipients who clicked a tracked link in the email.
Complaint Rate
How often people mark your mail as spam, relative to how much you send.
Content Filtering
Scanning the text, HTML, and attachments of a message for spam, phishing, or policy risk.
Conversion Rate
The percentage of recipients who completed the action the email was meant to drive.
Custom Domain
Sending and tracking mail from a domain you own, not a shared provider domain.
D
Dedicated IP
A sending IP used only by your traffic, not shared with other customers.
Deliverability
Whether mail reaches the inbox (or at least the mailbox) instead of spam, quarantine, or rejection.
DKIM
A digital signature on the message that proves the content was not altered in transit.
DMARC
A domain policy (plus reports) that tells receivers what to do when SPF or DKIM fail.
DNS
The lookup system that maps domain names to mail servers, keys, and policies.
Domain Reputation
How mailbox providers rate your sending domain based on past behavior.
Double Opt-in
A signup that only counts after the person confirms their address via email.
E
Email Client
The app or site people use to read mail, such as Gmail, Outlook, or Apple Mail.
Email Validation
Checking whether an address looks real and is safe to send to, before you mail it.
Engagement
Signs that people actually interact with your mail: opens, clicks, replies, and more.
Envelope
The SMTP-level sender and recipient used to route mail, separate from the visible From line.
ESP
A company or product that sends and manages email for you (Email Service Provider).
I
Inbound Email
Mail your system receives and processes, not only the mail you send out.
Inbox Placement
Where a delivered message lands: primary inbox, promotions, spam, or elsewhere.
IP Reputation
How mailbox providers rate a sending IP based on the traffic that leaves it.
IP Warming
Gradually raising send volume on a new or cold IP so providers learn to trust it.
M
Marketing Email
Promotional or newsletter mail sent to people who opted in, not triggered by a product action.
MIME
The format that lets email carry HTML, plain text, images, and attachments in one message.
MTA
Software that routes and delivers email between servers using SMTP.
MX Record
A DNS record that names which servers receive mail for a domain.
R
Rate Limiting
Caps on how fast you may send mail or call APIs, set by providers or your own stack.
RBL
A DNS-based blocklist queried in realtime while mail is handled (Realtime Blackhole List).
Reputation
The overall trust mailbox providers assign to your IPs, domains, and sending patterns.
Return-Path
The address that receives bounces; tied to the SMTP envelope sender.
Reverse DNS
A PTR record that maps an IP back to a hostname; receivers check this on SMTP connections.
S
Seed List
A set of test inboxes across providers used to check placement and rendering.
Shared IP
A sending IP used by many customers of an ESP or platform at once.
SMTP
The protocol servers use to move email across the internet (Simple Mail Transfer Protocol).
Soft Bounce
A temporary delivery failure that may succeed if you try again later.
Spam Trap
An address maintained to catch senders who mail without proper consent or list hygiene.
SPF
A DNS record that lists which hosts are allowed to send mail for your domain.
STARTTLS
A way to upgrade an SMTP connection from plain text to TLS encryption.
Suppression List
Addresses you must not mail: unsubscribes, complainers, hard bounces, and manual blocks.
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