Email deliverability is the ability to get legitimate email accepted and placed where recipients will see it. It is broader than simply pressing Send: a message can leave your platform, pass some technical checks, and still land in spam or be rejected. This glossary explains the terms business owners most often encounter when diagnosing delivery problems.
Deliverability and delivery
Delivery means a receiving system accepted the message. Deliverability means the message reached the intended inbox placement and was not filtered to spam or a lower-visibility tab. A message can be delivered but have poor deliverability. Start every investigation by identifying the exact symptom and a fresh example message.
Inbox placement
Inbox placement describes where accepted mail appears: inbox, spam, promotions, or another category. It is influenced by authentication, reputation, complaints, content, recipient engagement, and the receiving provider’s own filtering. There is no single setting that guarantees inbox placement at every mailbox.
SPF
Sender Policy Framework is a DNS TXT policy that authorizes systems to send using an envelope-from domain. It must have one policy record and stays within a ten-DNS-lookup limit. Use the SPF check guide to validate a real sender.
DKIM
DomainKeys Identified Mail adds a cryptographic signature to a message. The sending service signs it with a private key, while DNS publishes a public key at a selector record. A DKIM pass proves the signature verified; for DMARC it also needs appropriate domain alignment. See the DKIM record example.
DMARC
DMARC evaluates whether SPF or DKIM passed in alignment with the visible From domain. It can ask receivers to monitor, quarantine, or reject failed messages and can request aggregate reports. It is the policy layer that helps reduce domain spoofing. Read the implementation checklist before enforcement.
Alignment
Alignment means the authenticated SPF or DKIM identity matches, or is appropriately related to, the domain recipients see in the From address. A message can show SPF pass or DKIM pass yet fail DMARC if the identities do not align.
Sender reputation
Sender reputation is the receiving provider’s assessment of a sending domain, IP, and traffic pattern. Complaints, hard bounces, sudden volume changes, poor engagement, and unwanted mail can hurt it. Authentication supports reputation but cannot make irrelevant or unconsented email welcome.
Hard bounce and soft bounce
A hard bounce is a permanent failure such as a non-existent recipient. A soft bounce is temporary, such as a full mailbox or transient receiving-server issue. Remove or suppress hard bounces promptly and investigate patterns rather than treating every temporary failure as a permanent block.
Spam complaint
A spam complaint occurs when a recipient marks mail as junk. It is a strong negative signal. Make unsubscribe easy, send only to people who expect the content, and separate marketing from essential transactional mail. Complaints are often a list-quality or relevance issue, not a DNS issue.
Suppression list
A suppression list prevents future promotional mail to people who unsubscribed, bounced, complained, or otherwise should not be contacted. Preserve it during provider migrations and do not overwrite it with an imported list.
Authentication header
Message headers contain the receiving system’s SPF, DKIM, and DMARC evaluation. They are more useful than a sending dashboard when troubleshooting because they show what the recipient actually saw. Save the full headers with the timestamp and message ID.
DNS propagation
DNS changes can take time to appear across resolver caches based on TTL. Propagation can explain temporary inconsistent lookups, but it does not explain an invalid record, wrong host name, or unconfigured sender.
Run Beacon’s free domain check to review the public DNS foundation behind these terms.