Adestra put out an interesting report on what works in email subject lines and what doesn't. Character count, word count and the keywords themselves are all key ingredients, and the study compares variables across different types of emails.
For the report (via MarketingCharts), the firm analyzed 1.159 billion emails sent within the last year. They looked at the length of subject lines, as well as word selection.
"In the B2B world, it’s clear that either short or long subject lines work best. Short subject lines (<30 characters) perform strongly, as do long subject lines (>90)," write Parry Malm and Mark Bonner, the authors of the report. "The key point here is to consider what the end objective for your campaign is, and tailor your subject line around that."
"More benefits can be communicated by using more characters," they say. "In contrast to this, shorter, snappier subject lines that used 30 characters or less also performed well: this is the case for transactional or direct-action emails. Using a mid-range of characters in subject lines doesn’t yield strong results: the worst of both worlds. Anywhere between 30 and 60 characters is a dead zone, and will reduce the chances of opens and clicks in an email."
Whe picture for word count looks similar:
The report also examines different keywords for different types of emails. For discount offers, the word "sale" worked far better than "discount," "free," "save," or "voucher". For news emails, "news," "update," "breaking," "alert," and "bulletin" all worked better than "newsletter". "Issue" worked better than "forecast," "report," "research," "top stories," "interview," "video" "whitepaper" or "download". "Latest" worked better than "special," "exclusive," or "innovate".
For business emails, using words like "money," "revenue," or "profit" worked better than using words like "ROI," "asset," or "industry".
It's a pretty interesting study. You can download the whole thing here (it's free).