Email Deliverability

Email deliverability is the ability of your emails to actually land in recipients' inboxes, rather than in spam folders or nowhere at all. Getting a message "delivered" to the mail server is easy; getting it placed in the inbox depends on technical authentication, the sender's reputation, the quality of the list, and how recipients respond to previous messages.

The technical foundations

• SPF - a DNS record listing which servers may send email for your domain.
• DKIM - a cryptographic signature proving the message was not altered and really comes from the domain.
• DMARC - a policy telling receivers what to do when SPF or DKIM fail, and where to send reports.

Since 2024, Gmail and Yahoo require bulk senders to pass all three, offer one-click unsubscribe, and keep spam complaint rates below 0.3% - below-threshold senders are filtered regardless of content. Sending from a properly authenticated custom domain is now table stakes.

Why WiFi-captured lists need particular care

Addresses typed on a phone at a captive portal are typo-prone, so real-time validation at the point of capture (catching misspelt domains and disposable addresses) is what keeps hard bounces under the 2-3% level mailbox providers tolerate. Beyond that: send the welcome email promptly while the guest remembers signing up (recognition drives opens, and opens drive reputation), and stop mailing addresses that have been dormant for many months rather than dragging the whole list's engagement down.

Metrics to watch

• Bounce rate - hard bounces should stay low single digits; spikes poison reputation fast.
• Spam complaint rate - keep well under 0.3%.
• Open and click rates - the engagement signals mailbox providers weigh; a consented, recently active list (see opt-in rate) outperforms a big stale one every time.