A study analyzed more than 3 billion emails in four industries to determine which words were most and least effective. The industries included retail & B2C, conferences & events, media & publishing, and B2B/professional services & financial.

The authors warn that the words don't guarantee success and depend on the brand, but we can draw some conclusions about the results.

PR Daily summarizes the findings and shows two relevant charts:

Overall, email subject lines that include the words "thank you" have the highest above-average engagement levels (+62 percent)-perhaps because many automated, transactional messages include this phrase, such as email receipts sent by brands after customers complete online purchases.

Subject lines that separate topics with vertical pipes (e.g., "Sale now on | New lines added | Win trip to Dubai | Share your pics with #summer2015rules") also perform significantly above average (+47 percent).

Timeliness also tends to work well in email subject lines, with words such as "bulletin" (+32 percent), breaking (+27 percent), and "order today" (+27 percent) all boosting engagement.

The second and fifth bars are "vertical pipes" described above (four and three, respectively).

Discussion Starters:

• In Chapter 4, you read about catchy subject lines. How do these survey results match what you learned?
• Look at your 50 most recent emails. Which subject lines stand out to you? How many include successful words above?
• Practice writing a few subject lines with the successful words and vertical pipes.