Promo newsletters are often thought of as the simplest marketing tool out there. But they're exactly the type that anti-spam filters tend to trip up on. For your offer to reach as many people as possible, it's important to understand the basic reasons emails land in spam — from low domain reputation to an abundance of trigger words.
Stage 1. The subject line
The subject line is the "face" of your newsletter. If it doesn't grab attention within a second, the email is headed straight for the trash.
Why caps lock and trigger words hurt you Using all caps and words like "FREE" or "DEAL" sends a direct signal to 2026's anti-spam filters. Modern algorithms have gotten smarter: they evaluate not just individual words, but how they combine with punctuation. A pile of exclamation points next to the word "SALE" significantly lowers an email's chances of reaching the inbox.
Principles of a clickable subject line Use psychological triggers: intrigue, scarcity, or social proof. For more on how to make curiosity work in your favor, check out our piece on the psychology of email subject lines.
- Tip: Test the subject line together with the preheader. Use the preheader as a subheading that reveals more of the substance while keeping the subject line's intrigue intact.
Stage 2. Structure and content balance
Once the email is opened, you have 3 seconds for the reader to register your offer.
Ditch "image-only emails" Many brands still send a single giant banner. If a user has image loading turned off, or is using dark mode, they'll see nothing but empty space.
Rule: All important text (headline, terms, button) needs to be set as real text, not baked into an image. This matters both for display and for mail providers' scanning algorithms. Check out our 6 newsletter rules that work without a designer so your email looks professional even as plain text.
Product cards and auto-parsing If your email features several products, pay attention to how they're presented. To avoid coding every block by hand, you can set up automatic product card parsing. The system will pull current prices, photos, and descriptions from your site automatically.
Stage 3. Call to Action (CTA)
The button is the main point of interaction. If it's not visible or its text is vague, conversion drops.
Contrast and logic The button needs to stand out from the rest of the content while still fitting the brand's overall palette. What matters isn't just how it looks, but how it behaves across different email clients. Read our complete guide to building reliable buttons so your call to action doesn't fall apart in Outlook or mobile apps.
- Button text: Swap out a boring "Buy" for the outcome of the action, like "Get access to the sale" or "Pick your size."
Stage 4. Urgency and deadlines
Artificial pressure like "Hurry!" doesn't work anymore. Readers only trust concrete numbers.
Countdown timers Visualizing time is a powerful incentive. A countdown timer inside an email boosts CTR by 15–20% on average, since it creates a real sense that the deal is slipping away.
Checklist before you hit "Send"
Even pros make mistakes. To avoid embarrassing typos or broken links, run your email through our complete 100-point checklist.
What to check first:
- Deliverability: Whether the text contains spam trigger words.
- Display: How the email looks in Outlook (one of the trickiest clients). Learn more about the quirks of coding for Outlook so your design doesn't fall apart.
- Links: Whether UTM tags are in place.
You can build and test an email like this in Letteros — the builder lets you control every stage, from the preheader to mobile responsiveness, without needing a coder.