What is Email deliverability?
Email deliverability is the ability of your messages to reach recipients' inboxes rather than bouncing or landing in spam.
Also called: inbox placement.
Delivery and deliverability are different measures. A message is delivered when the receiving server accepts it; it is deliverable in the useful sense when it then lands in the inbox. A campaign can show a high delivery rate in a sending tool while much of it sits in spam folders.
Four factors decide it. Authentication: SPF, DKIM and DMARC on the sending domain; Google requires all three from anyone sending 5,000 or more messages a day to Gmail. Reputation: the domain's and IP's history of bounces, complaints and replies; see sender reputation. Volume: how many messages a mailbox sends and how fast that grows; see warm-up. Content: the words, links, images and formatting.
Of the four, the list is the foundation under reputation. Unverified addresses produce bounces, and bounces erode the reputation every later send depends on; see bounce rate.
Start with the DNS side in the SPF, DMARC and MX checker, then check copy in the spam word checker.