When you launch a campaign, some emails can end up in the "Spam" folder even with correctly configured domain settings. Modern email providers analyze not just sender reputation but the content of each individual message. A poor choice of words in the subject line or a broken email structure can trigger blocking.
In this article, we'll break down how spam filters work in 2026 and look at tools for pre-checking your content.
How modern spam filters work
Email services (Gmail, Mail.ru, Yandex Mail) evaluate emails based on a combination of factors. The main content analysis criteria fall into two categories.
1. Semantic analysisAlgorithms look for phrases typical of unwanted mass emails. A single suspicious word rarely triggers blocking, but a high concentration of them raises a message's spam score. Risky categories include:
- Promises of easy money and guaranteed income.
- Artificial urgency ("urgent," "today only," "don't miss out").
- Aggressive calls to action ("click now," "go immediately").
2. Structural analysisFilters react negatively to heavy use of capital letters (CAPS LOCK), excessive punctuation (!!!, ???), and flashy text formatting. They also check the ratio of text to images and whether there are any hidden links.
In 2026, providers use AI detectors that evaluate how "human" a piece of text feels. Templated messages generated by neural networks without any subsequent editing are more likely to get caught by filters and blocked by email services
Using neural networks to check your copy
To reduce the risk of being blocked, we recommend using neural networks that help make your copy sound more natural and remove spam triggers.
Useful tools:
- CopyMonkey and Retext.ai. Russian tools for rephrasing sentences. They help replace aggressive marketing phrasing with neutral wording without losing the meaning.
- GPTunnel. Provides access to current models (GPT-5, Claude 4.5) for adapting text to a specific tone of voice.
Effective prompts for checking your copy
To get a neural network to thoroughly check your email, use specific prompts:
1. Finding risky words and pressure tactics:
"Act as an email marketing expert. Analyze the email copy below. Find phrases that filters might interpret as aggressive selling or pressure on the reader. Build a table: risky phrase — risk level — suggested replacement."
2. Creating a safe subject line:
"Suggest 5 subject line options for a message about [your topic]. Constraints: up to 40 characters, no use of the words "sale," "free," or "deal." The subject line should spark curiosity but look like a personal message rather than mass advertising."
3. Making the text sound natural:
"Rewrite this text so it looks like it was written by hand, not by a neural network. Remove templated phrases ("unlock your potential," "unique opportunity," "in today's world"). Vary the sentence lengths, add a natural rhythm to the writing, and keep the business tone."
Tools for a pre-send check
Before sending an email to your entire list, you need to run a technical audit.
Mail-tester.com A tool for checking an email's technical health. It evaluates whether SPF, DKIM, and DMARC signatures are present and gives a score on the SpamAssassin scale. It helps catch major errors and check whether your IP address is blacklisted.
Postmaster Mail.ru and Yandex MailEssential tools for working in the Russian market. They provide deliverability and spam complaint statistics within specific mail systems, letting you track your domain's reputation over time.
Checking your email in the Letteros interface
The Letteros platform combines visual and technical auditing, eliminating the need for third-party tools.
Testing across 100+ email clients.This feature lets you see how your email displays across different versions of Outlook, mobile apps, and dark themes. It helps eliminate markup errors that could otherwise trigger blocking.
Built-in AI assistant.Helps generate subject lines and copy based on your prompts, while a built-in control system checks the markup and links for errors before sending.
Typography tool.Automatically fixes formatting errors and removes unnecessary characters from the email's code.
Pre-send checklist
- Subject line and preheader. No words in all caps (CAPS LOCK), no excessive punctuation, and no trigger words.
- Markup. A proper text-to-image balance is maintained (at least 60% text). All links point to trusted domains.
- Technical settings. SPF, DKIM, and DMARC signatures are configured and active.
- Unsubscribe link. Present in an accessible spot and working correctly.
High deliverability in 2026 depends on the balance between technical soundness and copy quality. Using the tools built into the Letteros platform lets you automate this process and make sure your email reaches the recipient.
Check your email right now: test how it displays across 100 email clients and use the assistant built into the Letteros interface.