Resources
Email Glossary
Plain-language definitions for email industry terms — ESP, transactional email, DMARC, SPF, DKIM, BIMI, IP warming, bounces, subdomains, subprocessors, and more.
ESP (Email Service Provider)
An ESP is the platform a business uses to send marketing or transactional email at scale. ESPs handle sender authentication, IP reputation, deliverability, and analytics.
Transactional Email
Transactional emails are one-to-one messages triggered by a user action — receipts, password resets, shipping notifications, and other operational mail.
Email Bounce
An email bounce is a message rejected by the recipient's mail server. Hard bounces are permanent failures; soft bounces are temporary.
SPF (Sender Policy Framework)
SPF is a DNS TXT record that lists the servers authorized to send email on behalf of a domain.
DKIM (DomainKeys Identified Mail)
DKIM is a cryptographic signature attached to outgoing mail that lets receivers verify the message has not been altered in transit.
DMARC
DMARC is an email authentication policy and reporting protocol built on SPF and DKIM. Bulk senders publish a DMARC record to tell receivers how to handle unauthenticated mail.
BIMI (Brand Indicators for Message Identification)
BIMI is a standard that lets verified senders display their logo next to their messages in supporting inboxes.
IP Warming
IP warming is the process of gradually increasing the volume of email sent from a new IP address so mailbox providers can build a reputation for it.
Email Subdomain
An email subdomain is a dedicated DNS subdomain (for example mail.example.com or send.example.com) used to isolate sending streams and protect a root domain's reputation.
Subprocessors
Subprocessors are third-party vendors a SaaS company uses to deliver its service. Privacy law usually requires SaaS companies to disclose them and obtain customer permission.
Apple Private Relay Email
Apple Private Relay creates a randomized, forwarding email address (ending in @privaterelay.appleid.com) that hides a user's real address from senders.
Promotional Email
Promotional emails are marketing messages sent to a list of subscribers — newsletters, product launches, sales, and re-engagement campaigns.
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