Loren McDonald

Email marketers seeking to increase their open and click-through rates would be wise to keep subject lines short and hyperlinks plentiful, according to recent analysis by EmailLabs.

The key findings: subject lines shorter than 50 characters in length, as well as an increased number of hyperlinks, led to increased open and click-through rates. Message size did not appear to be a significant factor in boosting rates, although messages in the 20 to 79 KB size range had slightly higher open and click-through rates than messages from 3 to 19 KBs.

Subject line lengths were divided into zero to 49 characters and 50+ characters. When analyzed, the zero to 49 character subject lines had an open-rate 12.5 percent higher than the 50+ character subject lines. Click-through rates for the zero to 49 character group were 75 percent higher than the 50+ group.

The differences in open and click-through rates were smaller but still distinct when evaluating the number of hyperlinks contained in the email. Emails with 25 or more links had an open rate of 12 percent higher than those containing fewer than 25 links, and a click-through rate of 29 percent higher than for emails with fewer than 25 links.

These results certainly support some long-held beliefs among email marketers. In general, email marketers should limit the length of their subject lines to less than 50 characters, and should include as many hyperlinks as possible. In addition to a shorter subject line being visible in its entirety in most email clients, recipients comprehend shorter subject lines more easily and quickly.

The more links there are, the greater the chances that one or more will resonate with the recipient and motivate them to click through. And while 25 links may sound like a lot, navigation and administrative-type links in best practices newsletters can easily reach 15-20 links by themselves.

For message size, 43 percent of client messages sent were in the 20 to 79 KB range, followed by 28.4 percent for 10 to 19 KB, 25.9 percent for 3 to 9 KB, 1.4 percent for less than 3 KB and one percent for 80 KB or larger. Messages in the 20 to 79 KB size range had open rates and click-through rates of 3.9 percent and 7.9 percent higher than messages in the 3 to 9 KB range. Interestingly, although only 1.4 percent of messages sent were less than three KB, those messages had the highest average open rate, bounce rate and unsubscribe rate.

Marketers shouldn’t be too concerned with the size of their messages, with our analysis not revealing any negative effect on performance from larger-sized messages. That being said, the general rule of thumb to try and limit messages to 40 to 50 KB is not a bad idea due to size limits on the receiving end.

Though these findings are compelling, it is essential that email marketers conduct split tests across key variables to determine what works best for their specific customers and subscribers. The EmailLabs analysis was based on the results of 23,475 email campaigns sent by more than 650 clients between January 1 and March 31, 2004.