linux - Using grep to find all emails

Question

How to properly construct regular expression for "grep" linux program, to find all email in, say /etc directory ? Currently, my script is following:

grep -srhw "[[:alnum:]]*@[[:alnum:]]*" /etc

It working OK - a see some of the emails, but when i modify it, to catch the one-or-more charactes before- and after the "@" sign ...

grep -srhw "[[:alnum:]]+@[[:alnum:]]+" /etc

.. it stops working at all

Also, it does't catches emails of form "Name.LastName@site.com"

Help !

Answer 1

Here is another example

grep -Eiorh '([[:alnum:]_.-]+@[[:alnum:]_.-]+?.[[:alpha:].]{2,6})' "$@" * | sort | uniq > emails.txt

This variant works with 3 level domains.