This is one of the oldest arguments in email marketing, and it has stayed unresolved for a simple reason: it is the wrong question. The honest answer, backed by decades of direct response testing, is that copy length should follow what you are asking the reader to do, not a stylistic preference either way.

The case for short copy

Short-form copy, roughly 50 to 150 words, works well when the reader does not need much convincing, when the offer or message is already familiar, or when the goal is a single, low-commitment click. It creates curiosity rather than resolving it, and it respects a reader's limited time, which matters given that mobile email sessions average only around 10 seconds.

The case for long copy

Long-form copy earns its place when a reader genuinely needs more information before acting, a considered purchase, a detailed explanation, or a story that needs room to land. A well-cited 2015 experiment by direct response copywriter Bob Bly, along with decades of similar direct mail testing summarised by Who's Mailing What, found long copy consistently outperforming short copy specifically in categories where the audience has real, unanswered questions before they will commit.

What decides it for a specific send

• What is the ask? A single click to a familiar product needs less copy than a considered decision.
• How much does the reader already know? A cold audience often needs more context than an existing customer.
• What does your own audience actually do? A/B testing your own list beats applying someone else's industry rule.
• What is the brand voice? A brand built around storytelling earns permission for longer copy than one built around quick, punchy updates.

The rule of thumb worth keeping

As long as necessary, but no longer, is a genuinely useful standard precisely because it refuses to pick a side. The goal is never length for its own sake in either direction. It is copy that resolves exactly as much doubt as the specific ask requires, and stops there.

How to test it properly

Split your list, send a short version to one segment and a long version to the other, with an identical call to action across both, then compare open rate, click rate, and conversion rate rather than just the first two. A short version sometimes wins clicks while a long version wins actual conversions, because it has already answered the objections a shorter email left unaddressed.

Frequently asked questions

Is short email copy always better for mobile?

Not automatically. A long email can still work on mobile if it is well-structured with clear subheadings and scannable sections, though it does need more deliberate formatting than a short email to hold attention on a small screen.

How long is too long for a marketing email?

There is no fixed ceiling. The better question is whether every section is still resolving a genuine doubt the reader has, rather than restating a point already made.

Should welcome emails be short or long?

Often shorter and warmer works best for a first email, since a brand-new subscriber has not yet earned the trust needed for a long read. Save longer, more detailed content for once the relationship is established.

What matters more than length?

Whether the copy, at whatever length, is specific and resolves genuine doubt rather than padding. Vague long copy underperforms specific short copy every time.

Mail Blaze is an email marketing platform specialising in email engagement, and our AI tools can help draft both short and long variants of a campaign so you can test what your own audience actually responds to.

Try drafting both a short and long version of your next campaign using Mail Blaze's AI tools, included on every plan.

P.S. If you are not sure which length fits a specific send, describe it to us and we will give you a straight answer, not a generic rule.