The Letter Is Back: Direct Mail Marketing in B2B

Why is it worth rethinking the sales letter?

Anyone who wants to approach a potential business customer for the first time today quickly runs into limits. In Germany, promotional emails without consent are generally prohibited even when sent to companies, and calls are allowed only where interest can be justified. Messages on professional networks get lost in a flood of similar requests. At the same time, many businesses’ mailboxes have emptied as invoices, bank statements and advertising have moved online.

This assessment answers the question: When is a promotional letter by post a sensible route in B2B today, and how must it be designed to lead to a conversation? We first clarify the terms and look at market figures. Then the adstock model explains why media have carryover effects of different lengths, and we look at what studies show about mail and email. We weigh two views, place the legal framework and end with a process for a small letter campaign.

A letter is the only advertising medium the recipient has to pick up before throwing it away.

What is direct mail marketing, and how large is the market?

Direct marketing refers to advertising aimed at individual, named recipients that is meant to trigger a response, such as a call, an appointment or an order. By post, this mainly means addressed promotional letters, known in the trade as mailings, and catalogs. They differ from unaddressed door drops that go to all households or businesses in an area. In B2B, almost only the addressed letter to a specific person in a specific business counts.

With its Dialogmarketing-Monitor, Deutsche Post surveys every year how much companies in Germany spend on advertising. For the 2026 edition, Statista surveyed 1,500 marketing decision-makers on behalf of the postal company. According to the study, the net advertising market grew by 2.7 percent to 45.3 billion euros in 2025, driven mainly by online marketing. Companies spent 5.8 billion euros on direct mail, the same as the year before.

The figures have a limitation you should know. The study is published by a company that earns money from letters. It also does not distinguish between advertising to consumers and to business customers. But it shows that the letter is not a disappearing medium but a stable part of the advertising market, while other classic media are shrinking.

Why does advertising have a carryover effect? The adstock model

To understand what a letter does differently from an email, a model from advertising research helps. The adstock model goes back to the British advertising practitioner Simon Broadbent. It describes advertising as a stock that is replenished with every contact and then slowly depletes. An ad that appears today works not only today but also in the following days and weeks, with decreasing strength. How fast it fades is called the decay rate.

The everyday analogy is a note on the fridge. An email is like a sentence someone says in passing: it is heard or not, and an hour later it is forgotten. A letter that stays on the desk or goes into the file is like the note. It reminds you as long as it is there.

Zantedeschi, Feit and Bradlow (2017) measured exactly these decay rates for different media. A retailer had randomly held out some customers from each campaign. This created a series of field experiments from which the effect of each medium could be estimated. Both emails and catalogs showed positive effects. But the catalogs affected purchasing behavior for much longer than the emails. The study concerns consumers, not business customers, and a single retailer.

What do studies show about mail and email?

The most thorough study so far on which medium works for whom comes from Valenti, Srinivasan and Yildirim (2024). Over four years, they analyzed the purchase and contact data of almost 85,000 customers of an international cosmetics retailer in six countries, including Germany, plus data from almost 24,000 customers of an American apparel retailer. Their result: promotional letters mainly helped acquire new customers. Emails, by contrast, worked mainly with existing customers. A field experiment with all 120,000 of the cosmetics retailer’s customers in Italy confirmed this relationship.

Drawing on earlier work, the authors cite the tangibility of the letter, the feeling of being valued and the space for more information as reasons. People who do not yet know a supplier need exactly that. Existing customers already know the supplier and respond to the cheaper, faster email. The authors also cite a cost estimate according to which an email campaign costs about 38 percent of a letter campaign.

Togawa and colleagues (2024) provide a possible reason for the stronger effect. In field and lab experiments, printed coupons led to more redemptions than online coupons. This was mediated by stronger cognitive engagement with the content. The effect was larger among people with low brand attachment. That too fits a letter to someone who does not yet know the sender.

Two views: does the letter work in B2B too?

The findings come mostly from consumer retail. For business markets there are two readings. The first says the letter is less effective there. Valenti and colleagues themselves refer to a B2B study by Wiesel and colleagues that found no effect of direct mail on sales. In addition, letters in larger businesses often end up in a mailroom and never reach the recipient.

The second reading says the letter fits B2B even better if used correctly. Business customers receive few personal letters, the number of potential customers is small and each one is worth a lot. A well-made letter to twenty target accounts is something quite different from a mass mailing to a thousand addresses. Then there is the legal framework, which is considerably more open for letters than for email and phone.

I consider the second reading the better one, but only for a narrow use: the personal letter to a few carefully selected target accounts, with a clear occasion and a simple way to respond. As mass advertising to purchased addresses, the letter probably does achieve little in B2B. Neither is proven for small businesses. The evidence only supports a reasoned assessment.

The letter is no longer a mass medium. It is the most personal tool a small sales team still has.

What does the law require?

In Germany, two sets of rules apply to advertising side by side, as the article on data protection in sales describes in detail: the Act Against Unfair Competition (UWG) and the General Data Protection Regulation (GDPR). For addressed promotional letters to companies, the situation is comparatively simple. The UWG does not require prior consent for letters. Letter advertising becomes inadmissible when it is apparent that the recipient does not want it, for example after an objection.

Under the GDPR, direct marketing can be a legitimate interest on which processing a name and address can be based. The recipient has the right to object to use for advertising at any time and must be informed of this. If their data was not collected from them directly, they must also be informed about its source and purpose. In the channel traffic light from the article mentioned, the letter without prior contact is therefore amber: usually possible, with the right to object and information.

In practice this means: every letter states in one closing sentence where the address comes from, what it is used for and how the recipient can object. An objection is recorded in the CRM immediately and respected permanently. This is legally required and at the same time a sign of decency that recipients notice.

What does a small letter campaign to target accounts look like?

From the findings follows a use that suits small and midsize businesses: few recipients, a personal letter, a clear occasion, a simple way to respond. Selecting recipients starts with the ideal customer profile, as described in the article on defining target customers.

1. Select recipients

   20 to 50 businesses that match the ideal customer profile and, for each, one named person who decides. No purchased mass address lists.

2. Find an occasion

   A concrete reason why you are writing right now: a new regulation in the industry, a completed project nearby, an expert article on a question these businesses have.

3. Write the letter

   One page, personal salutation, the occasion in the first paragraph, then the benefit for the recipient in two or three sentences, a handwritten signature. Add a working aid, such as a checklist.

4. Offer a way to respond

   A personal direct line, a short web address or a QR code to online booking. How online booking works is described in the article on online appointment booking.

5. Plan the follow-up

   Where there is a justified interest, a call can follow after about ten days. Where there is not, a second letter with a new occasion follows after four to six weeks.

How the conversation after a response should be structured is described in the article on the first sales meeting. The study by Valenti and colleagues also points to a second, often overlooked use of the letter: it suits customers who have not bought for a long time. How to spot them early is described in the article on why customers leave.

What you can do this week

• Select ten target accounts that match the ideal customer profile, each with one person who decides.
• Find a shared, concrete occasion for these ten.
• Write a one-page letter with the occasion in the first paragraph and a handwritten signature.
• Add a closing sentence on the source of the address, purpose and right to object.
• Set a simple way to respond: direct line, short web address or online booking.
• Create the source “letter” in the CRM so responses can be attributed all the way to the order.

Conclusion: when does the sales letter pay off in B2B?

The guiding question was when a promotional letter by post is a sensible route in B2B and how it must be designed. Market figures show that the letter has remained a stable medium. The adstock model and the measurements by Zantedeschi, Feit and Bradlow (2017) explain why printed advertising has a longer carryover effect. The study by Valenti, Srinivasan and Yildirim (2024) shows that mail works mainly with people who do not yet know the supplier.

For small and midsize businesses this results in a clear, narrow use: the personal letter to a few target accounts, with an occasion, a benefit and a simple way to respond, legally clean with a note on the right to object. As mass advertising, the letter remains questionable in B2B. As a personal first approach, it is one of the few routes that combine attention, legal certainty and respect for the recipient.