Email Deliverability and Why Your Messages Vanish

Authentication is now effectively mandatory

Three DNS records establish that you are entitled to send from your domain.

SPF lists which servers may send on your behalf. DKIM adds a cryptographic signature proving the message was not altered and came from an authorised sender. DMARC tells receiving servers what to do when the first two fail, and where to send reports.

Major providers tightened requirements substantially in 2024, particularly for bulk senders, and messages without proper authentication are now routinely rejected or filtered rather than merely scored down.

If you send any volume of business email and have not configured these, that is almost certainly your problem.

Sender reputation

Receiving systems build a reputation for your sending domain and IP based on recipient behaviour: opens, replies, deletions without reading, and above all spam complaints.

Reputation degrades with high bounce rates, spam complaints, and sending to addresses that have been inactive for a long time. It recovers slowly.

Sending from a shared IP means other senders' behaviour affects you. Dedicated IPs give control and require sufficient volume to maintain reputation.

List hygiene

Never buy lists. Beyond the legal problems in most jurisdictions, purchased lists contain outdated addresses and spam traps that damage reputation immediately and lastingly.

Use confirmed opt-in where practical. Remove hard bounces immediately and suppress addresses that have not engaged in an extended period.

Make unsubscribing easy and honour it promptly. People who cannot find the unsubscribe link mark messages as spam, which is far more damaging than losing the subscriber.

Content factors

Content matters less than authentication and reputation but is not irrelevant. Excessive capitals, aggressive punctuation, misleading subject lines and image-only messages with no text all attract filtering.

A sensible text-to-image ratio and a plain-text alternative version help. So does consistency in sending patterns — a sudden large send from a domain that normally sends little looks anomalous.

Transactional versus marketing

Separate them, ideally on different subdomains. Marketing email attracts complaints; transactional email — receipts, password resets — must arrive reliably.

Keeping them separate means a poorly received campaign does not prevent customers receiving their order confirmations.

Diagnosing problems

Set up DMARC reporting and read it. It shows what is being sent using your domain and whether it authenticates, including sources you did not know about.