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Translated from German; if the versions differ, the German version applies.
Not legal advice: Legal content on this page appears only as verbatim quotations from statutes, court rulings or authority papers, with their source; quotations from German texts are our working translations. We do not assess them ourselves, and no lawyer has reviewed this page. It is no substitute for legal advice in your individual case.
Newsletter landing in spam: finding the causes
When readers report that the newsletter is in their spam folder, there is rarely just one reason. Mailbox providers assess many signals; senders can influence most of them. Work through the following steps in order – from the technical foundation to the list itself.
Step 1: Is the email properly authenticated?
The most common cause, and the easiest to fix. Open a test issue in a Gmail or Outlook.com mailbox and display the headers or the “original”. It shows whether SPF, DKIM and DMARC passed.
- SPF fail or softfail: the sending platform is missing from the SPF record.
- SPF permerror: the record needs more than ten DNS lookups, or the domain has more than one SPF record.
- DKIM missing or belonging to the wrong domain: the sending platform signs only with its own domain instead of yours.
- DMARC fail: neither SPF nor DKIM is aligned with the visible sender domain.
Gmail requires all senders to have at least SPF or DKIM, and bulk senders all three; Microsoft recommends SPF, DKIM and DMARC to all senders. Instructions: Setting up DMARC, Requirements of the mailbox providers.
Step 2: Are recipients complaining?
Every click on “Report spam” counts against you. For the spam rate in Postmaster Tools, Gmail names a limit of 0.3% and recommends staying permanently below 0.1%; Yahoo also names 0.3%. With 10,000 recipients, 0.3% already means 30 complaints.
Feedback loops show where complaints come from: some mailbox providers report spam complaints back to registered senders. RFC 6449 describes how senders use these reports as an indication of whether recipients still want to receive emails – and respond, for example via the sign-up process, the frequency or the maintenance of the list. The usual causes:
- Recipients do not remember signing up (addresses from prize draws, old lists, trade fairs).
- Unsubscribing is hidden or cumbersome – “Report spam” is then the quicker way.
- Content or frequency no longer match what was promised at sign-up.
Step 3: How many emails bounce?
Bounces are a clear signal of a poorly maintained list. The enhanced status codes under RFC 3463 distinguish permanent errors (class 5, e.g. 5.1.1: the mailbox does not exist) from temporary ones (class 4, e.g. 4.2.2: mailbox full). Addresses with permanent errors should be removed from the list immediately; most sending platforms do this automatically. If the number suddenly rises, check whether an old list was imported.
Step 4: Is the server on a blocklist?
Blocklists collect IP addresses or domains from which spam was sent. RFC 5782 describes how such lists are distributed via the DNS and how receiving servers can query them for incoming emails. Anyone who sends via a sending service often shares IP addresses with other customers; a listing then affects all of them. Your sending service should be able to tell you whether its addresses are listed and what it is doing about it. Anyone who sends themselves checks this with the operators of the lists.
Step 5: Has the sending volume changed abruptly?
Google advises increasing sending volume slowly and avoiding sudden jumps; even an immediate doubling can lead to rate limiting or a poorer reputation. Typical triggers are the first send via a new platform, a new sender domain or a large list that has not been written to for a long time. Spread such mailings over several days and start with the recipients who clicked most recently.
Step 6: Is the list still maintained?
Addresses that have not opened or clicked anything for years are a risk: in our experience they often belong to mailboxes that nobody reads any more. It has proved useful to ask such recipients specifically whether they still want the newsletter and otherwise to remove them from the list.
The German Data Protection Conference (Datenschutzkonferenz, DSK) writes in its guidance on direct marketing: “In the interest of transparent data processing, advertisers are in particular recommended, in the case of consents that have not been used for more than two years, to renew the information or the consents themselves as a precaution […].” (guidance on direct marketing, section 3.5, p. 13, our translation). Quotations from German laws and authority papers on this page are our working translations; only the German wording is authoritative (see the German version of this page). Not legal advice.
Step 7: Content and structure
Content plays a role, but less often than is frequently assumed. Check:
- Is there a text version alongside the HTML version?
- Does the email consist almost entirely of one large image?
- Do links point to domains that themselves have a poor reputation (such as link shorteners)?
- Do sender name, subject line and content fit together?
What you should not do
- Ask recipients to “whitelist” you instead of fixing the cause. That helps individuals, not deliverability.
- Switch sender domain to escape a poor reputation. Mailbox providers also assess new domains – usually cautiously when they have no history.
- Mailing old or third-party lists all at once. Many recipients do not remember signing up and report spam (step 2); unknown addresses increase the bounce rate (step 3).