Subject line never ending questions & stats

I have been in the cold email space for over 9 years and have access to data across millions of emails. A lot of ppl fixates over subject lines so in the hope that this helps someone I am sharing what the data actually shows, plus a few things that correlated with better performance.

1. Shorter subject lines win, but only slightly

→ 10-19 characters: ~30% open rate 
→ 40-60 characters: ~23% open rate

This is based on US data (~400 companies, no agencies, first email only). Outside the US the trend is the same but even weaker. In the end a lot of the data averages out.

2. Open rates are a messy metric to begin with

→ The tracking pixel does not always load 
→ Sometimes it loads automatically (Apple Mail Privacy Protection can inflate numbers)

Nevertheless, they are the only thing you have that helps you estimate inbox placement. 
Inbox placement tests are not representative of the real world and reputation data is impossible to get (looking at you Postmaster Tools). 

Ignore daily fluctuations in your open rates. 40%? ok, 45%? sure. 56% even better, back to 45%? don’t freak out. What you should look out for are:

→ sudden drops that stay. Look for blacklists, check content, check authentication
→ steady decline week over week. Potentially losing reputation or being put to spam and not taken out 
(who does that for cold email anyways).

And before people comment use reply rates… 

Go to an A/B testing calculator. 
Put in your base line conversion, let’s say 2% (your reply rate per email sent). 
Then put in ~20% relative minimum detectable effect 
(so how much of a drop or gain you want to be able to see). 

Come back with the number here. 
This will be the number of prospects you need to detect those 20%. 
It will not be 100, 1000, and not even 10000.

That’s how many prospects you need PER group. 
How are you able to detect any deliverability issues in time?

3. Subject lines that correlated with top performance

→ First name included but don’t use it in the subject AND first sentence, otherwise you repeat yourself 
→ Internal sounding, boring, or opening a curiosity loop (incomplete information) 
→ Seamless subject lines that flow into the first sentence (pattern breaker)

First name in subject lines feels overused (at least for me personally) BUT the data across millions of emails still shows that it lifts open rates. 

One last tip:
Don’t over-optimize the subject line Past “short, boring, not salesy” there isn’t much left to squeeze. If you are starting out I would put that energy into your list and your offer instead. That is where the actual multiplier for your reply rates is.

Are you tracking open rate or purely rely on reply rate?