Deliverability
The ability to consistently land in the inbox rather than the spam folder or being rejected.
Deliverability is the share of your email that reaches the inbox, not just the receiving server. Delivery and deliverability are different numbers: a message counts as delivered when the receiving server accepts it, even if it then lands in spam where the subscriber never sees it. Mailbox providers decide placement using authentication (SPF, DKIM, DMARC), the reputation of your domain and sending IPs, spam complaints and how recipients engage with your mail.
How to measure deliverability
Your platform's delivery rate (accepted divided by sent) only shows bounces and rejections. For inbox placement, use what mailbox providers report: Google Postmaster Tools shows the spam rate Gmail users report for your authenticated domain, and Microsoft SNDS shows data for sending IPs you control. Google asks senders to keep that spam rate below 0.1% and never reach 0.3%.
Seed-list tests, which send a campaign to test inboxes, give a rough placement estimate but cannot show how your real subscribers' inboxes treat you. A drop in clicks or replies on an otherwise healthy list is often the first sign of a placement problem.
What your email platform controls
Part of deliverability belongs to your platform: the reputation of its shared IP pools, how quickly it lets new accounts scale, and whether it makes custom-domain authentication easy. The rest is yours: who you mail, how often and whether they asked for it. Switching platforms rarely fixes a list or content problem, and moving means building a sending history on the new platform from scratch.
Common deliverability mistakes
Treating a 99% delivery rate as proof that mail reaches the inbox. Buying or scraping lists, which brings bounces, spam traps and complaints. Hiding or breaking the unsubscribe link: Google and Yahoo require bulk senders to support one-click unsubscribe (RFC 8058) plus a visible link, and people who cannot find one press the spam button instead. Sending a sudden large volume from a new domain instead of increasing volume gradually.
Sources
Related terms
Sender Reputation
A score inbox providers assign to your sending domain and IP based on engagement, complaints, and bounces.
DKIM (DomainKeys Identified Mail)
A cryptographic signature added to outgoing emails that proves the message really came from your domain and was not tampered with.
SPF (Sender Policy Framework)
A DNS record that lists which servers are allowed to send email on behalf of your domain.