Email Deliverability
Quick definition
Email deliverability is the ability of your emails to reach recipients' inboxes rather than being rejected, filtered to spam or lost. It depends on both technical setup and how recipients respond to your mail.
Delivered is not the same as in the inbox
A message counts as delivered when the receiving server accepts it. It can still be placed in a spam or promotions folder. Deliverability is about reaching the inbox, which is why sender reputation and recipient behavior matter as much as the technical hand-off.
Factors that affect it
- Authentication: SPF, DKIM and DMARC are email authentication and policy mechanisms, specified in RFC 7208, RFC 6376 and RFC 7489, that receiving servers can use to check whether a message really comes from the domain it claims.
- Sender reputation: complaints, bounces and recipient engagement all feed into how mailbox providers treat your mail.
- List quality: permission-based sign-ups, confirmed addresses and regular removal of invalid ones.
- Content and sending patterns: sudden jumps in volume, misleading subject lines and broken links can count against you.
- An easy way to unsubscribe, which makes recipients less likely to mark mail as spam.
Practical habits
- Send only to people who asked to hear from you.
- Confirm new sign-ups.
- Clean the list regularly.
- Increase sending volume gradually when starting with a new domain or provider.
- Watch bounce and complaint rates.
- Keep your authentication records up to date.
Requirements change
Mailbox providers publish their own sender requirements and update them over time. Check the current guidelines of the providers your recipients use rather than relying on fixed thresholds.
Example
A store imports a list of 50,000 purchased addresses and sends a promotion to all of them in one day. Many addresses are invalid or never agreed to hear from the store, producing bounces and spam complaints that damage its sender reputation and can hurt delivery of later messages, including those to its genuine customers.