"Our emails end up in spam" describes a symptom, not a problem. The possible causes are few and well known, they turn up in roughly the same order of frequency every time, and most of them are fixed without changing anything large.
The trouble is that nobody tells you. The message reports as "sent", the recipient never sees it, and the cost surfaces weeks later — a quote with no reply, an invoice chased twice, a customer convinced you never got back to them.
Here are the seven, from the most common to the rarest.
1. Authentication is missing, or incomplete
This is the first cause by a wide margin. Without SPF and DKIM configured and aligned to the domain the recipient sees in the "From" field, filters have no way to tell you apart from anyone writing in your name.
The detail that catches nearly everybody: SPF can report "pass" while DMARC still fails, because the check passed on the sending platform's domain rather than on yours. Technically authenticated, and in practice a stranger.
You recognise it by looking at the headers of an email that did arrive: the authentication lines say what the recipient saw. It is fixed in an afternoon of work on DNS records.
2. The domain is new, or has not sent for months
Filters trust history. A domain registered three weeks ago has none, and a domain that has not sent for a year has lost the one it had.
There is no shortcut: reputation is built by sending little, to people who open and reply, and growing slowly. The classic mistake is the opposite — new domain, first campaign to two thousand addresses, reputation burnt on the first attempt.
3. The sending IP address has a bad reputation
If you send from the shared server of a cheap host, you share an IP with everybody else on it, including whoever is sending questionable things. IP reputation is collective.
You recognise it like this: mail from the same domain arrives fine at one provider and badly at another, and the problem appeared without you changing anything. The fix is sending through a proper mail service rather than from the website's server, and it is one of the most concrete reasons to reconsider where the mail is hosted.
4. The content looks like a campaign, even when it is not
Filters read the message too. What raises suspicion, in order:
- an email made of one large image and two lines of text;
- masked links, or shorteners hiding the real address;
- attachments nobody was expecting, especially compressed files;
- subject lines in capitals, or full of exclamation marks;
- the classic promotional vocabulary: free, urgent, last chance, click now.
An invoice written like an invoice gets through. An invoice that looks like an advertisement does not.
5. There is no easy way to unsubscribe
This applies to bulk communication rather than to individual emails, but it weighs: the large providers' rules for high-volume senders require simple unsubscription that works in one click and is honoured quickly.
A form that asks people to log in before unsubscribing is, to a filter, a bad signal. And it matters more than politeness: people who cannot unsubscribe mark you as spam instead, and complaints count for far more.
6. The list is old and full of dead addresses
Sending to mailboxes that no longer exist produces bounces, and a high bounce rate is one of the worst signals a domain can send.
Worse: some abandoned addresses are reactivated as traps, precisely to identify senders working from stale lists. A bought list, or one not cleaned for years, almost certainly contains some.
The practical rule: if a contact has opened nothing in two years, they are not a contact. Removing them improves everything else.
7. A deeper technical problem
Less frequent, but real: a mail server configured without a reverse DNS record, a hostname that does not match, an expired TLS certificate on the mail server, or a compromised domain somebody is quietly sending from.
That last case is more common than it sounds and has a precise symptom: legitimate mail suddenly gets worse with nothing having changed, and the authentication reports show volumes that are not yours.
Where to actually start
The order that resolves things fastest:
- read the headers of an email that landed badly — they say what the filters saw, without guesswork;
- fix authentication and alignment: on its own this resolves the majority of cases;
- turn on DMARC in observation mode and read the reports for two or three weeks, to see who sends in your name;
- separate the streams: bulk communication should not leave from the same place as everyday business email;
- clean the list before the next campaign, not after it.
None of these steps requires changing email provider. You change the provider only if, at the end of this list, the provider is the problem — which happens, but rarely.
If you would rather start from a diagnosis than from attempts, that is exactly the first step of business email: SPF, DKIM and DMARC.