Resources
Email deliverability glossary
The terms that matter when you send email at scale — explained in plain English.
A living reference. New terms added over time.
- SPF (Sender Policy Framework)
- A DNS record that lists which mail servers are allowed to send email on behalf of a domain. Receiving servers check it to reject spoofed senders. A typical record looks like
v=spf1 include:amazonses.com ~all. - DKIM (DomainKeys Identified Mail)
- A cryptographic signature added to each email's headers. It lets the receiver verify the message genuinely came from (and wasn't altered since leaving) the sending domain. DKIM uses a set of CNAME records with long tokens.
- DMARC
- Domain-based Message Authentication, Reporting and Conformance. A DNS policy (published at
_dmarc.domain) that tells receivers what to do when SPF or DKIM fail — none, quarantine, or reject — and where to send aggregate reports. - Bounce
- An email that could not be delivered. A hard bounce means the address doesn't exist (permanent); a soft bounce is temporary (full mailbox, server down). Hard-bounced addresses should be suppressed to protect sender reputation.
- Complaint
- When a recipient marks your email as spam or reports it to their provider. High complaint rates damage deliverability, so complaints should be tracked and the affected recipients suppressed.
- Transactional email
- Email triggered by a user's action in your product — password resets, receipts, order confirmations, verification codes. It's expected, time-sensitive, and central to your product's function (as opposed to marketing email).
- Sender reputation
- A score mailbox providers (Gmail, Outlook, etc.) keep for your sending domain/IP, based on delivery history, bounce and complaint rates, and engagement. Good reputation means inbox placement; poor reputation means spam folder or rejection.
- SES (Simple Email Service)
- Amazon's email-sending service. It provides high-deliverability infrastructure for transactional and bulk email, with per-email pricing and detailed delivery, bounce, and complaint feedback.
- Warm-up
- Gradually increasing your sending volume over time so mailbox providers build trust in your new domain or IP. Sending a large volume cold is a common cause of poor initial deliverability.
- Suppression list
- A list of addresses you stop sending to — typically hard bounces and spam complaints. Keeping a suppression list protects your reputation and is required for good deliverability.
- Inbox placement
- The share of your emails that land in the primary inbox (versus the spam or promotions tab). It's the ultimate measure of deliverability health.
- API key
- A secret token your application uses to authenticate to the SendHQ API. Treat it like a password — keep it server-side and never expose it in client-side code.