Your emails land in spam: how to diagnose delivery
Work through email delivery problems in the right order so you fix authentication and sending reputation instead of rewriting subject lines that were never the cause.
The symptom is vague and the causes are not
A customer mentions they found your mail in spam. Your own test to a colleague arrived fine. Open rates have been sliding for a month and nobody connected the two. This is how a delivery problem presents itself and the vagueness is the reason most businesses start by rewriting subject lines.
Delivery has three layers. Whether the receiving server accepts the message at all. Whether it trusts the sender. And whether it believes recipients want it. Subject lines sit a long way down that list. Diagnosing in the wrong order wastes weeks because every change you make takes days to show an effect.
What diagnosis costs and what it cannot buy
No amount of spending buys guaranteed inbox placement. Mailbox providers make that decision per message and per recipient using signals they do not publish in full. Anybody promising placement is selling something they do not control. What is buyable is the removal of every reason a provider has to distrust you.
The work splits three ways. A DNS and authentication pass which is a technical job measured in hours and usually one-time. List hygiene which is ongoing. And a sending behaviour change which costs nothing in cash and a great deal in discipline. Where you pay somebody for this the fee attracts GST at 18% as a service.
Time is the real cost. Reputation recovers on the mailbox provider's schedule and that is weeks of consistent low-volume sending rather than days. Budget the calendar before the money.
When this is not your problem to solve
Do not run a deliverability programme if your list was bought or scraped. The diagnosis is already complete. Recipients who never asked for your mail will report it and no authentication record repairs that. The honest answer is to stop sending to that file and rebuild a list from people who consented. Businesses spend heavily on technical remediation to keep a list that is the cause rather than the victim.
Do not invest here either if you send a few hundred messages a month to existing clients and one of them found a message in spam once. At that volume you have an incident and not a pattern. Confirm your authentication records are correct and move on.
This work earns its place when you send regularly at volume to a list you built and the trend is downward across providers. That is a reputation problem and reputation problems respond to method.
The diagnostic sequence
Start with authentication because it is binary and cheap to check. Confirm SPF lists every service that sends on your behalf. Confirm DKIM signs your mail with a key published in your DNS. Then confirm DMARC exists and that your mail passes it with alignment on the visible from domain. Google and Yahoo both now publish sender requirements that treat authentication as a condition of bulk delivery rather than a recommendation.
Next read what the providers tell you. Google Postmaster Tools reports domain reputation and spam complaint rates for mail you send to Gmail addresses and that single dashboard answers questions no amount of internal testing will. Check your sending domain and IP against the major public blocklists at the same time.
Only then look at behaviour. Separate transactional mail from marketing onto different subdomains so a bad campaign cannot take your invoices down with it. Suppress contacts who have not engaged in a long window. Add a one-click unsubscribe header because the bulk sender requirements expect it and because a visible unsubscribe is what stops somebody pressing report instead.
How to tell whether it is recovering
Delivered rate is the flattering number and it is nearly useless here. A message accepted by the server and filed in spam counts as delivered. Your platform will show a healthy figure throughout a complete placement failure.
The metrics that matter are spam complaint rate and domain reputation as the provider reports it plus click rate on your most engaged segment. Complaint rate is a leading indicator and reputation is the lagging one. Watch them per provider rather than in aggregate because a problem at one mailbox provider disappears inside a blended average and that average is what reassures people for the month before everything stops working.
The common mistake
The expensive error is changing the sending domain to escape a bad reputation. It feels decisive and it resets the problem rather than solving it. A fresh domain has no reputation at all which providers treat with suspicion and the volume that damaged the old domain damages the new one within weeks. You have also split your sending history in two and lost the only record that would have shown recovery.
The second error is testing by sending to your own team. Mail from your domain to colleagues on the same domain often bypasses external filtering entirely. It proves the message composed correctly and nothing else. Test to addresses at the providers your customers actually use and treat your own inbox as the least informative result you have.
This guide explains how something works. It is not legal, tax or financial advice, and rules change. Confirm anything regulatory with a qualified professional before you act on it.