it is true. when i was in my phd studies, i have a committee member, mid-age male associate prof. I never got replied unless I directly called him up. He was crazy bad at self management. one day when I visited him at UMich, I happened to see his email exchange box. WTF! He has tons of, for sure more than 1000 emails sleeping as UNREAD.
i will try my best to reply all emails in each single day. for some emails i cannot deal with or give my answer immediately, I will flag it, and insert it into my to do list.