Between 3 and 8, depending how to interpretate the question. I have some email accounts that I rarely use but still use for certain purposes, and a couple of accounts I check very often. So depends on the interpretation/frequency of "using".
PS: I deleted this message and then re-posted it in order to change my answer on the poll, but apparently this isn't possible and your initial answer either is gone or stands without the option to vote again. I miscounted when I first replied
, forgot one account I rarely use but still own which made the total amount rise above 7.