It took me just a minute to think about it before I realised the most recent transactions I had completed, due to email, were all triggered events. This morning there was the anniversary of my donation to Wikipedia, to keep the lights on, and a payment to reserve seats on an upcoming fight, as i hadn't done so in the last month. There was even a very tempting wine offer that twisted my arm because my monthly subscription had gone in for the past couple of months but I hadn't ordered any fizz for Christmas.
You know the kind of campaign. It's been so long since you did something and really you should be doing it again by now, so here's a prompt and maybe even an offer too. Or last time you ordered you went for X, it's been a month and you're still in, say, Economy, for a limited time you can upgrade for half the normal cost. There are also the very obvious emails that link purchases, such as "we hope you're enjoying your new bicycle, isn't it time to get some lights for it now the nights are drawing in?"
Of course there are other more immediate emails, such as checking in at an airport to be greeted by an email's worth of vouchers, although (and I have no data to back this up) I rather suspect these are in the midst of being replaced by app notifications.
So, if you ever need a stat to back up the fact that your organisation should not just be spraying and praying email all over the place, and should be focusing on triggered events, you now have the figure that will hopefully prove convincing.
Build in triggers around behaviour, make anniversaries for people, understand what they might need from a purchase a month ago or what they haven't yet upgraded from that interaction and be charming as you help them out with their missing product or service. Nobody minds being understood. When you have an email inbox packed with generic offers that reveal what a store is selling far more than any understanding of what you may need, it's nice to receive something tailored specifically for you.
Whether you convert or not, personalised email is the way forward and there's nothing more personalised than an offer triggered around your last, or at least a previous, interaction with that brand.