The research was done by Alchemy Worx of England. Their study was fascinating, mostly because it was contrary to what I believed to be true.

According to the study which was done on 646 subject lines across 205 million messages, shorter subject lines generated higher open rates, but much lower click-to-open rates.

Longer subject lines earned a much higher click-to-open rate, but much lower open rates.

The open rates and the click-to-open rates evened out at between 60 and 70 characters, where neither metric was optimized.

The highest click-to-open rates started at 16 words and went all the way up to 25 words in the subject line. That's between 110 and 140 characters.

Click-to-Open Rate
Number of clicks divided by the number of opens

I would have considered 25 words to be a very long subject line ... but not anymore. Based on these findings, you will see Recognized Expert using much longer subject lines in our emails.

Read the Alchemy Worx white paper

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Very interesting article. Goes to show how powerful segmenting and testing emails can be.

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this article really makes you pause & re-evaluate writing your subject lines.

as a general rule, i tend to keep my subject lines short ('round 10 - 15 words) but highly relevant to the message. it's a balance of relaying message content but with enough curiosity for the recipient to click open. once they're in i insert 2 relevant links (1 above scroll, 1 towards the end). the conversions have worked quite well.

with this new information, it's certainly worth testing longer subject lines.

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Nice article there BOb, As an Email Marketing expert, I use short titles but unique and verbatic to boost readage.

It has been working for me and I believe it will work for everyone. Short titles that are catchy is much productive than long boring titles.

That is very interesting. As mic10 has said, relevence is vital.

but think about it.. this makes a lot of sense actually... think about those opening email with longer subject lines have been "pre-qualified".. longer subject lines reveal more information of the content of the emails. so if they open it.. they are truly interested in the content.. thus higher click-to-open rate.

shorter subject lines may not have enough information.. quite a few of them open it out of curiosity and may not be genuinely interested in the content of the emails.. which inflate the open rate and dilute the click-to-open rate...

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Nice one.

Is there any place where there is a list of words that should not be used in subject line so that email doesn't be marked as SPAM?

We can't just consider subject line length as an factor for good open rate. The content of subject should be given also equal importance.

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the problem with longer subject lines are that they might get cut off