What emailers can learn from a #10 envelope

Email and direct mail teams test a lot of the same things — copy, personalization, volume, gift amounts. 

But direct mail has been at it for decades longer, and the testing data runs deep.

Your team is probably in the thick of year-end planning, and your email and mail programs are about to hit the same donors at the same time. 

It’s a good window to compare notes, and here’s what’s worth borrowing from snail mail.

Your long email might actually work?
Email has drifted hard toward brevity, and for a lot of programs, that instinct is often proven right. 

It makes sense: Attention spans are short, and drawing the reader in from the jump to sign a petition or make a gift is crucial.

Direct mail has decades of data to suggest otherwise, and it’s worth exploring.

A PI World analysis of 2025 mail results found that donor appeals and higher-value offers performed well with longer, story-driven copy.

Try this: Pick one high-stakes appeal this fall and test the long vs. short theory. Every program’s file responds differently! 

The only way to know whether longer copy moves the needle on your bigger asks is to test it against your current instinct.

The format direct mail never abandoned
Direct mail’s top-performing nonprofit format is still a personalized letter in a #10 envelope.

It’s not flashy, and leads with text that reads like one person writing to another.

We’re already seeing this in email. KUOW saw 28% more donations when they tested a plain-text style appeal against a designed HTML template.

There’s a technical case for it now, too. Gmail, Apple, and Outlook are using AI to summarize emails based on the first 150–200 characters of live text, not images. 

Try this: Test a stripped-down, personal-looking email against your current template on your next appeal. Same copy, same ask: just remove your logo, or a CTA banner you might typically use in an appeal, and see what happens.

Test whether more emails actually means more revenue
The frequency question never goes away: are we emailing too much, or not enough? 

Direct mail teams have long used holdout testing to measure whether skipping a random segment on a campaign or two results in a change in giving.

It’s a simple concept. If a control group that received two fewer mailings gave at a lower rate than everyone else, then the higher volume was well worth the effort.

Try this: Hold out 5-10% of your list from 1-2 emails in an upcoming campaign and compare revenue per contact after 30 days. It’s the easiest way to find out whether your send volume is earning its keep.

The bottom line
Copy length testing, format testing, holdout methodology — direct mail teams have been running these plays for decades, and all of them work in email.

I’ll be the first to admit it’s easy to get stuck in the habits of your own channel. 

But your donors don’t think in channels, and the smartest thing you can do heading into year-end is look at what’s working next door.

Check our events list for more or reply to this email to submit one for consideration.

‘Til next time!
Sara