How to prevent your emails from going to spam during holidays (Gmail & Outlook)

Every year during the holiday season, Gmail and Outlook spam filters become stricter. What landed in the inbox without issues in October suddenly ends up in spam in November and December. This isn't random. It's a deliberate choice by these providers to protect users from the massive wave of marketing emails during Black Friday, Cyber Monday, and the holidays.

For businesses sending marketing campaigns or transactional emails, this is a disaster. Think of Black Friday or Cyber Monday campaigns that nobody sees, newsletters with holiday offers that disappear, or order confirmations that never arrive. With proper preparation, you can prevent these problems.

Why do spam filters get stricter during holidays?

During the holiday season, businesses send massively more emails than usual. Gmail and Outlook spam filters see explosive growth in sent messages, along with an increase in spam and unwanted marketing.

What normally passes through the filter gets checked much more critically in November and December. An email that landed in the inbox throughout the year can suddenly end up in the spam folder due to:

• Excessive sales language like DISCOUNT DISCOUNT DISCOUNT or LAST CHANCE
• Too many capital letters in the subject line
• Excessive use of exclamation marks
• Aggressive discount claims (90% OFF!!!)
• Urgency words like NOW, IMMEDIATELY, or TODAY ONLY

You probably see this kind of language regularly in your own spam folder. Emails from unknown webshops and fake businesses using exactly these words. Gmail and Outlook learn from these patterns and during holidays, they become extra critical—even toward legitimate businesses using the same language.

These stricter filters typically remain active until early January, when things calm down again. But the damage may already be done: a damaged sender reputation, lost customers, and missed revenue.

How to prepare your campaign

The best way to avoid spam problems is good preparation. Start well before Black Friday or the holidays with optimizing your emails. Here are the key steps:

Spread your send volume for campaigns and newsletters

A sudden spike in your send volume is a red flag for spam filters. Do you normally send 1,000 emails per day and suddenly increase this to 50,000? That looks suspicious to providers like Gmail and Outlook.

Send your campaigns in phases instead of all at once. For example, divide your list over multiple days or send in batches spread throughout the day. This keeps your send volume consistent and prevents you from suddenly being seen as a spammer.

Test your emails beforehand

Use tools to check if your email contains spam-sensitive words. At Lettermint, we developed Spam Insights that analyzes your email structure and shows a spam score. This way you can see directly which elements might cause problems and test before sending the newsletter to your full list.

Additionally, you can use our test email addresses for free to see how your email is processed without it counting toward your monthly usage.

Keep your mailing list clean

Only send to people who have been recently active. Old, inactive addresses lead to more bounces and spam complaints. The chance that old contacts who haven't interacted with your brand for months or years will mark your email as spam is high.

A damaged sender reputation has major consequences. Not just during the holidays, but also in the months after. Even important transactional emails like order confirmations can end up in spam.

Watch your word choice

Avoid excessive sales language in your emails. Words like FREE, SALE, DISCOUNT DISCOUNT DISCOUNT, or LAST CHANCE trigger spam filters quickly. This also applies to terms like BUY NOW, LIMITED OFFER, or FLASH SALE.

Also avoid too many capital letters in your subject line and don't use more than one exclamation mark. A natural writing style has less chance of being blocked by spam filters than aggressive marketing language.

Conclusion

Spam filters become stricter every year during Black Friday, Cyber Monday, and the holidays. By preparing your emails well, spreading your send volume, and keeping your mailing list clean, you prevent your campaigns from ending up in spam.

Always test beforehand with tools like Spam Insights that analyze your spam score and our test email addresses. This way you know for sure that your emails arrive where they belong: in your customers' inbox.