Subject lines that get opened

A subject line has one job: to get the message opened. It does not have to sell, summarise or be clever.

Clarity against curiosity

The old rule said curiosity drives opens. It holds for people who do not know you and fails as soon as a relationship exists.

With a maintained warm list, the plain statement almost always wins. "2027 price list is out" beats "You will be surprised". The reason is simple: with known senders, people decide on usefulness rather than on stimulus.

Six patterns that measurably carry

1. Concrete benefit with a number. "Three grant schemes for heat pumps, August position"
2. Deadline. "Registration closes Friday", provided the deadline is real.
3. Direct question about the problem. "Your quote has been sitting two weeks?"
4. News with a bearing. "New price display rules, what changes for you"
5. Outcome of a case. "How one firm cut scrap by 40 per cent"
6. Plain announcement. "Your invoice, your appointment, your delivery" for service mail.

What does not work despite universal advice

• Spam word lists. Words like free or win no longer trigger filters. Filters assess sender reputation and recipient behaviour. A good sender may write "free"; a bad one is filtered anyway.
• First name in the subject. Slightly positive in warm lists, clearly negative in cold outreach, because it reads as automated bulk.
• Capitals and exclamation marks. They lower opens in almost every measured case.
• The subject as a summary. Say everything in the subject and you give no reason to open.

Testing properly

A test on the whole list is not a test, it is a send. Split instead: ten per cent get subject A, ten per cent subject B; wait four hours, not thirty minutes; the remaining eighty per cent get the winner; and note the question tested, not just the winner.

Below 2,000 addresses this procedure is statistically weak. There, test the same pattern across several sends and compare over a quarter.

The link to the content

A subject that promises more than the message delivers produces an open and an unsubscribe. The open rate rises and the list shrinks.

So never judge the subject alone. Always look at the pair of open rate and unsubscribe rate. If both rise together, the subject was too loud.