Why your emails are marked as spam

The four things that decide whether your mail reaches an inbox, in the order worth checking.

Mail you send arrives in recipients' spam folders. Applies to shared, reseller and Premium hosting.

Deliverability comes down to four things. Work through them in this order — the first two account for most cases.

1. Authentication

Receiving servers check whether you are authorised to send as your domain. A domain that fails these checks is filtered almost everywhere.

SPF — Set your SPF record
DKIM — enable it under cPanel → Email Deliverability
DMARC — Publish a DMARC record

cPanel → Email Deliverability validates all three and shows what is wrong. Start there; if it reports a problem, nothing else you change will matter much.

2. How you are sending

Authenticate over SMTP. Sending unauthenticated adds points to the spam score immediately — see Fix "550 Please turn on SMTP Authentication".

Do not use PHP mail(). It relays via the server hostname while your application claims a different From address, and receivers read the mismatch as spoofing — see Enable PHP mail() and Send WordPress email over SMTP.

Send from an address on your own domain. A From address of noreply@gmail.com sent from your server fails alignment.

3. Content

Spam scoring reacts to recognisable patterns:

Subject lines in capitals, or heavy exclamation marks
Bulk-mail phrasing — "act now", "limited time", guaranteed returns
A message that is one large image with almost no text
Shortened links such as bit.ly, which hide the destination

See Fix "550 This message was classified as SPAM".

4. Reputation

Sending IP reputation is largely handled for you: outbound mail routes through a dedicated relay rather than your account's shared IP, so a neighbour's problems do not become yours — see How outbound mail is relayed.

Your domain's reputation is yours, and it is damaged by:

A compromised mailbox sending spam — see Fix the 550 5.7.1 [SS] rejection
Sending to purchased or scraped lists
High complaint rates from recipients marking mail as spam

Bulk sending

Do not send campaigns from a normal mailbox. It will be scored as spam regardless of content, and hit your sending limits. Use a dedicated bulk service — it handles unsubscribes and reputation, which is the whole point.

Diagnosing a specific message

Get the full headers from a message that was filtered. Authentication-Results shows whether SPF, DKIM and DMARC passed, and the spam score shows how close it was — which tells you whether you have one problem or several.