Answer by Farhan for grep out unique senders from a huge list of emails

To get total number of emails, run:

grep From: /home/user/mail/new | wc -l

to get the count of emails from root, run this

grep ^From /home/user/mail/new | grep root\@hostname.com | wc -l

now (Total emails) - (emails from root) = actual number of emails from total emails.