email_check.sh

#!/bin/bash

if [ ! -z "$(find ~/.mail/*/INBOX -type f)" ]; then
  printf '📥  '
  for box in `ls ~/.mail | grep -v temp`; do
    emails=$(find ~/.mail/$box/INBOX -type f | wc -l)
    [ $emails -ne 0 ] && printf '%s:%d ' ${box:0:1} $emails
  done
  printf '~\n'
fi

...the [] character on line four is an emoji (I use 📥)