Delivered is not the same as inbox
Deliverability is about whether your emails reach the place a recipient will actually see them. It is easy to confuse with simple delivery. A message counts as delivered when the receiving mail server accepts it. Whether it then appears in the main inbox, a promotions tab, or the spam folder is a separate question, and that second question is what deliverability usually refers to.
This distinction explains a common frustration: a sending tool reports (hypothetically) that nearly all messages were delivered, yet many recipients say they never saw them. Both can be true if the messages were accepted and then filtered into spam.
Why legitimate messages land in spam
Mailbox providers handle huge volumes of unwanted mail, so they filter aggressively. They use many signals, and the exact rules are not public and change over time. Honest senders can be caught for reasons that are not always obvious. Broadly, the factors fall into several groups.
Sender reputation
Providers keep track of how mail from your sending address, your domain and the servers you use has been received. Frequent complaints, many bounces and sudden spikes in volume tend to hurt reputation. A long record of mail that people open and reply to tends to help. New senders have no history, so they often have to build trust gradually.
If you use an email service that sends for many customers, you may share some infrastructure with others, which is one reason to choose reputable services and follow their rules.
Authentication
Authentication is a set of technical records that let receiving servers check that a message really comes from the domain it claims. You may see the names of such methods in your email tool’s setup instructions. In general terms, they confirm that:
- The server sending the message is permitted to send for your domain
- The message was not altered on the way
- There is a published policy for what to do with messages that fail the checks
Setting these up usually involves adding records to your domain’s settings, which your domain host or email service can explain. Missing or incorrect records are a frequent and fixable cause of poor placement. The same checks also protect recipients, because they make it harder for scammers to impersonate you, which links to the problem of phishing emails.
List quality
Mailing people who did not ask for your message, or whose addresses are wrong or abandoned, produces complaints and bounces. Old addresses can even be reused as traps by providers to identify careless senders. This is a main reason to avoid purchased lists, and the practices of email list building focus on consent for exactly this reason.
Engagement
Providers watch how recipients behave. Messages that are opened, replied to or moved out of spam are good signs. Messages that are deleted unread, ignored for months or marked as junk are bad ones. A list that has not been cleaned for years can drag down results for the whole sending domain.
Content and format
Content matters less than people often fear, but it plays a part. Things that can raise suspicion include:
- Misleading or deceptive subject lines
- Large images with little text
- Excessive capitals and exclamation marks
- Broken or mismatched links, or links to disreputable sites
- Missing unsubscribe options
- Attachments from unfamiliar senders
There is no magic list of forbidden words. Writing clearly and honestly, in the way you would write to a customer you know, is the best general approach. Principles for this appear in the article on email subject lines.
Sending patterns
A sudden jump from fifty emails a month to fifty thousand looks odd to a filter. Gradual increases, consistent schedules and a recognizable sender name and address help. Changing sending domains or tools frequently can reset your reputation.
What you can do
Because the rules are not published and vary between providers, nobody can guarantee inbox placement. But sensible habits generally help.
- Send only to people who opted in, and record how and when they did.
- Make unsubscribing easy. A person who can leave quietly is less likely to report you as spam.
- Set up authentication for your sending domain using your email service’s instructions.
- Use a consistent sender name and address that recipients recognize.
- Remove bounces and long-inactive subscribers from time to time.
- Start slowly if you are new or if you are moving to a new tool, rather than sending to the whole list at once.
- Keep messages honest and relevant. Subject lines should match the content.
- Watch complaints and unsubscribes. Rising numbers suggest a problem with expectations or frequency.
- Ask subscribers to add your address to their contacts, if they wish. This is a polite request, not a guarantee.
Testing and monitoring
Many email tools show bounce and complaint rates. Some offer inbox placement tests, though results can differ from what real recipients see. Another simple check is to send a message to a few accounts at different providers, including ones you own, and see where it lands. If a pattern appears, such as consistent spam placement at one provider, investigate settings and consider whether recent changes in content or list source explain it.
Open rates are an imperfect signal because some mail apps load images automatically or hide tracking, so use clicks and replies alongside them. For more on interpreting numbers, the guides to web analytics and conversion rate are helpful.
What it means for you
Deliverability is not a trick to defeat filters. It is mostly the result of ordinary good practice: asking permission, sending useful messages, keeping your list tidy, and setting up the technical basics. When problems persist despite this, your email service’s support team or a domain host can help diagnose them. For the wider picture of lists, content and measurement, see the overview of email marketing.