The two ways subject lines fail
Subject lines fail in one of two ways. The first is being forgettable: "Our latest products" gets deleted unread. The second is being deceptive: "Re: your order" on a message that is not a reply, or "70% off" when the email contains no discount. The second failure is worse, because a materially misleading subject line is a per-email violation under CAN-SPAM, and because it trains your audience to ignore you.
Write the body first
A subject line is a summary of an email that already exists. If you write the subject before the body, you are guessing. Write the body, then ask: "in one short line, what is the single most important thing in this email?" That line is your subject. The discipline of summarising forces you to have an actual point.
Respect the character budget
Most opens happen on mobile, and mobile clients clip subject lines around 30-40 characters. A 65-character subject line is invisible past the first half on most phones. Keep the key noun — the product, the offer, the question — in the first 25 characters, and treat 50 as the absolute ceiling.
The one-line summary test
Before sending, imagine a recipient forwarding your email to a friend with the subject line pasted above it. Does the combination make sense, or does the subject promise something the body does not deliver? If the latter, one of them is wrong. This test catches both deception and vagueness in one pass.
What genuinely works
- Specificity: "The 1.7L kettle is back in stock" beats "We have news".
- Curiosity with a payoff: "Why your water bottle leaks (and the 2-minute fix)".
- Numbers that are real: "5 settings, 3 colours, 1 decision".
- The recipient's own context: "Your basket is saved" to someone with an abandoned cart.
What to never do
- "Re:" or "Fwd:" prefixes on messages that are neither.
- Urgency that is not real: "FINAL WARNING", "ends tonight" sent weekly.
- Discounts that are not in the email.
- Subject lines so long they are 50% ellipsis on mobile.
A subject line that summarises honestly and fits in 40 characters will outperform a clever one that misleads — because opens are worthless if the email does not deliver what the subject promised.
Written by the CopyForge AI team. Drafted with AI assistance, then reviewed and fact-checked by a human before publishing.