Well, I just rolled over my email collections from the the 2016-2018 election time.
What I do is that I keep all of the emails from every candidate, PAC, special interest groups that get sent to me during an election cycle.. I initially signed up for back in 2008 for 3 lists- OFA, DCCC, DSC. I later added my Rep and Senators. My email address has been passed on to lots of candidates, special interest and the Dem (any/all of the party lists).
This evening I rolled my list over to close it out and start a new one. My email total for this past election cycle: 24,760 . This is up from the 2014-2016 cycle of 14,865, and the 2012-1014 cycle of 6,559.
Brief statistics, at 365X2 is 750 days, divided int 24,760 equals 32.57 emails per day.