[18.01.2018 12:48:56]darkraven@darkraven-pc:~/Prog/temp/regexps$ cat f3
maksim@mail.ru
pashka777@gmail.com
Vanya@gmail.com
super.star@ya.ru
@q.q
Difors@rhy3ta.com
petya@MAIL.com
perch1k@ml.COM
r@r.rrr
[18.01.2018 12:48:57]darkraven@darkraven-pc:~/Prog/temp/regexps$
[18.01.2018 12:48:58]darkraven@darkraven-pc:~/Prog/temp/regexps$ cat f3 | grep -P '^[a-z0-9]+@[a-z]+\.[a-zA-Z]{3}$'
pashka777@gmail.com
perch1k@ml.COM
r@r.rrr