Glossary
Plain definitions of the email terms that appear in Sendly's documentation, dashboard and API errors
Email carries a lot of vocabulary from the 1980s, and most of it is only explained in RFCs. These are the terms you will meet in Sendly's dashboard, in an API error, or in a conversation about why a message did not arrive — each defined in a paragraph, with a link to the part of the documentation that shows you what to do about it.
Every entry says what the term means in general and, where the two differ, what Sendly specifically does with it. Where Sendly does not implement something, the entry says so rather than describing the general case as if it were ours.
Sending domains
Sending domain
The domain your mail claims to come from, and the thing you verify.
SPF
A DNS record listing who is allowed to send for your domain.
DKIM
A cryptographic signature proving a message was not altered in transit.
DMARC
Your published policy for mail that fails SPF and DKIM.
Return-Path
The envelope address bounces come back to, which is not the From address.
MX record
The DNS record saying which server receives mail for a domain.
Deliverability
Deliverability
Whether your mail reaches the inbox, as distinct from being accepted.
Sender reputation
The score mailbox providers keep on your domain and your sending IPs.
Bounce
A delivery failure, and why the hard and soft kinds are not the same problem.
Complaint
What happens when a recipient presses the spam button.
Suppression list
The addresses Sendly refuses to mail, and why you cannot simply delete them.
IP warm-up
Building a sending reputation gradually rather than all at once.
Consent
Double opt-in
Confirming a subscription by email before you mail anyone.
List-Unsubscribe
The header that puts an unsubscribe link in the mail client itself.
Sending
Transactional email
A message sent to one person because of something they did.
Marketing email
A message sent to an audience, which needs consent and an unsubscribe.
Campaign
One broadcast to a list or a segment, at a time you choose.
Workflow
An automated sequence that reacts to data and behaviour.
Segment
A rule-defined slice of your contacts that keeps itself current.
Template variable
The placeholder a contact's own data is substituted into.
Idempotency key
What makes retrying a send safe rather than a duplicate.