Email Deliverability Basics

Sent is not the same as delivered

An email platform reporting that a message was "sent" only means it was handed to the recipient's mail server. Deliverability describes whether it then reaches the inbox rather than the spam folder, or is rejected outright. Mailbox providers make that decision using signals about the sender, the list and the content, and they do not publish exact rules. Anyone who promises guaranteed inbox placement is overstating what is knowable.

Sender authentication

Receiving servers want evidence that a message really comes from the domain it claims. Three standards do this work:

• SPF lists the servers allowed to send mail for your domain.
• DKIM adds a cryptographic signature that shows the message was not altered and was authorised by the domain.
• DMARC tells receivers what to do when SPF or DKIM checks fail, and can report failures back to you.

Major mailbox providers publish sender requirements that include authentication, particularly for bulk senders; check the current guidelines from the providers your audience uses. Most email platforms guide you through adding the required DNS records for your domain.

Sender reputation

Mailbox providers build a picture of each sending domain and address based on past behaviour. Positive signals include recipients opening and replying; negative ones include spam complaints, messages to non-existent addresses and sudden spikes in volume. A new domain has no history, so it is wise to start with modest volumes to engaged recipients and increase gradually.

List quality

The single most controllable factor is who is on your list.

• Collect permission. Only email people who have agreed to hear from you about the topic you are sending.
• Use a clear sign-up process. Some businesses use confirmation emails to verify addresses and intent.
• Remove bounces promptly. Repeatedly sending to invalid addresses harms reputation.
• Do not buy lists. Purchased lists contain people who did not opt in, raise complaint rates and may breach privacy law.
• Prune inactive contacts. Consider a re-engagement message and then stop emailing people who never respond.

Content and design

Modern filters weigh content less crudely than old "spam word" lists suggested, but common-sense practice still helps: a clear subject line that matches the message, a recognisable sender name, a balanced mix of text and images, working links, and a visible unsubscribe option. Avoid misleading subject lines. In many jurisdictions, commercial email must identify itself honestly and provide an opt-out; see messaging consent and compliance basics.

Engagement and cadence

Providers observe whether recipients interact with your messages. Segmenting so that people receive relevant content, keeping a consistent sending schedule and honouring unsubscribes quickly all support healthy engagement. Beware of abrupt changes such as suddenly emailing a dormant list of thousands.

Transactional vs marketing email

Transactional messages, such as receipts and booking confirmations, are triggered by an individual's action and expected by them. Marketing messages are promotional. Many businesses separate the two streams so that a marketing problem does not affect receipts.

A simple deliverability checklist

• Authenticate your sending domain with SPF, DKIM and DMARC.
• Use a real reply-to address that someone monitors.
• Send only to people who have opted in.
• Include a working unsubscribe link and process requests promptly.
• Warm up new domains with small, engaged audiences.
• Remove hard bounces and review complaint rates.
• Monitor open and reply patterns as trends, not absolute truths.

Reading the numbers with care

Open rates have become less reliable because some mail apps pre-load images, so treat them as a rough indicator. Replies, clicks, complaints and unsubscribes are more informative. For how email fits into a broader follow-up system, see email and SMS marketing.

Keep learning

• Email & SMS MarketingLearn how email and text messages support nurturing, reminders and notifications, with consent and deliverability done right.
• Marketing AutomationLearn how triggers, actions and conditional logic automate follow-up, onboarding, reminders and retention.
• Advertising & CampaignsLearn search and social advertising basics, tracking, audiences, budgets and the ad-to-CRM journey.