Does email performance drop when more marketers are sending emails?

Last week we noticed that email performance dipped when send volume was highest, but is that a widespread trend or a one-off fluke due to the marketing overload that only happens during a free-for-all like Cyber Monday? That was our question, here’s our answer.

The Goods
To find our answer we looked at over 700,000,000 emails sent by 100 resorts and hotels over the last three years. Our analysis is based on the assumption that if more of those 100 resorts were active on a given day, other brands (not in our sample) would be too. So we:

1. Found the average send volume of every day since Jan 1, 2014.
2. Compared that day’s volume to the average of the 10 days before and after.
3. Grouped the results by how far above/below average the send volume was.
4. Found how far above/below average performance was for each group.

For example, the first bar on the left in the chart below means that on days where marketing volume was less than 50% of normal, the open rate on that day was 3.4% above average.

As noted above, on days that saw significantly lower volume (less than half of average) the open rate was 3.5% higher than normal. On days that saw 150% of typical send volume the open rate was 3.2% lower than normal.

What This Means
As we suspected, on days where send volume was highest open rate dropped and visa-versa, but the difference was small. Remember, a difference of +3.4% on a 20% open rate is just +0.7 percentage points or a difference of 1034 opens instead of 1000.

So, yes, there’s a difference, but not a massive one. We also need to remember that if many brands are sending on the same day, there may be more important reasons for that which take priority over a small bump in open rate.