Missing authentication
Without SPF, DKIM and DMARC, recipients cannot check that the message really comes from you. That is the most common reason.
Guide · Email
Why association emails go to spam. And what helps.
The invitation has gone out, but half the members find it in spam or not at all. There is almost always an identifiable reason. This guide shows the most common causes, the large providers’ rules and how to narrow down the problem yourself.
By Paul Czichos, consulting and project support at czichos.net GmbH · Updated
The most common causes
Why emails go to spam. Six reasons messages end up in spam.
Usually several come together. The first three are technical and can be fixed in an afternoon.
Poor sender reputation
The server you send through is on a blocklist or shares its address with a spammer.
No matching reverse DNS
The mail server’s IP address has no name in DNS, or the name does not match. Large providers treat this as a warning sign.
Many complaints
When recipients mark your messages as spam, providers remember. Google gives 0.3% as the upper limit.
Outdated lists
Dead addresses and abandoned mailboxes that providers use as spam traps cost reputation.
The content
A single large image, link shorteners, loud subject lines, no unsubscribe link. Rarely the only reason, but often an additional one.
The large providers’ rules
Gmail and Outlook sender requirements. What Google, Yahoo and Microsoft require.
Since February 2024, Google and Yahoo have enforced binding sender requirements, and Microsoft followed for Outlook.com in May 2025. Since November 2025, Gmail has increasingly rejected messages that do not meet them.
- For all senders: SPF or DKIM, valid reverse DNS for the sending IP address, encrypted transmission and a complaint rate below 0.3%.
- From 5,000 messages a day to Gmail addresses, additionally: SPF and DKIM, DMARC at least with p=none, authentication aligned with the sender domain and, for marketing and subscribed messages, one-click unsubscribe as defined in RFC 8058, honoured within two days.
One-click unsubscribe consists of two headers set by your sending system:
List-Unsubscribe: <https://news.your-association.org/unsubscribe?id=…>, <mailto:unsubscribe@your-association.org>
List-Unsubscribe-Post: List-Unsubscribe=One-Click
The guide to SPF, DKIM and DMARC explains how to set them up. The guide to member mailings from your own domain shows how a circular meets these rules.
Five-step diagnosis
Diagnosing delivery problems. How to narrow down the problem yourself.
Work through these in order. Most cases are solved in the first two steps.
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Step 1: Send a test message to Gmail
Open it with “Show original”. Does it say PASS for SPF, DKIM and DMARC? If not, you have found the cause.
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Step 2: Check blocklists
Look up your mail server’s address with an aggregator. The guide to blocklist checks explains how, and what to watch out for with Spamhaus. Blocklist monitoring such as secMonitor does this continuously.
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Step 3: Check reverse DNS
Your mail server’s IP address should have a name that points back to the same address. If your mailbox is hosted by a provider, they take care of it.
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Step 4: See the providers’ view
Google’s free Postmaster Tools show your domain’s complaint rate, authentication and reputation. A verification record in DNS is all you need.
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Step 5: Check list and content
How many bounces did the last mailing have? Is there a visible unsubscribe link? Does the message contain more text than images? If in doubt, send a plain-text version for comparison. A separate guide shows how to analyse delivery rate and bounces.
Do it yourself or have it done
Improving deliverability yourself? You can fix most causes yourself.
For an association with one domain and a mailbox provider, the solution almost always lies in the DNS records and in keeping the list clean.
Fix it yourself
If you send through a provider
- Add SPF, DKIM and DMARCDone in an afternoon with your provider’s instructions and our guide.
- Google Postmaster ToolsFree, and the best source for how Gmail sees your mail.
- Clean up the listRemove hard bounces and follow up with addresses that haven’t responded in years.
Have it done
If you run your own mail system
- Your own outgoing serversReputation, reverse DNS, blocklists and DKIM keys are then your job every day.
- An account suddenly sends spamA single hijacked mailbox can ruin the reputation for everyone if nobody stops the sending.
- Proof towards recipientsWhen someone claims they received nothing, only complete tracking of every message helps.
On our own behalf: we earn money from the second column. If your association sends through a mailbox provider, the three DNS records and a clean list are almost always enough.
Common questions
Spam and deliverability FAQ. What associations ask.
Why do my emails go to spam in Gmail?
Usually authentication with SPF, DKIM or DMARC is missing, or the sending address has a poor reputation. “Show original” in Gmail tells you whether authentication passes. Google Postmaster Tools show reputation and complaint rate.
What have Google and Yahoo required since 2024?
From all senders: SPF or DKIM, valid reverse DNS, encrypted transmission and a complaint rate below 0.3%. Anyone sending more than 5,000 messages a day to their users also needs SPF and DKIM, DMARC and, for marketing and subscribed messages, one-click unsubscribe.
Does it help to avoid words like “free”?
Hardly. Modern filters mainly assess authentication, reputation and recipient behaviour. Content rarely decides on its own.
Why do our messages reach some people but not others?
Every provider filters differently and uses different blocklists. If only one provider is affected, its own tools help, such as Postmaster Tools for Google or SNDS for Microsoft.
Do we need our own IP address?
Most associations don’t. A dedicated address only pays off with large, regular volumes, because its reputation then depends entirely on you. For small volumes, a well-maintained shared address from a reputable provider is usually better.
Sending and delivery with secMail
Outgoing mail runs through sender classes that set how much goes out via which address. If an address gets throttled, sending switches over. secMail holds suspicious accounts so that everyone’s reputation stays protected. Deliverability is visible per receiving provider, and every message can be traced.
Your messages aren’t arriving? We’ll take a look.
Send us a short description and, if you have them, the headers of an affected message. We will tell you what is behind it, even if you fix it yourself afterwards.
No obligation and no contract. We usually reply within one working day. secMail is priced according to your mail setup, on request.
Prefer to reach us directly? Send an email · call 030 994048000