Check valid email addresses

Filter invalid email addresses using shell script:

Check for valid domain names

cat email_addr.txt | cut -d "@" -f 2 | sort -u| xargs -I {} host -t MX '{}' | grep "not found";

Check for email address RFC compliance

cat email_addr.txt | egrep "^[a-Z0-9,\!\#\$\%\&'\\*\+/=\?\^\\_\`\{\|\}\~\-]+(\.[a-Z0-9,\!\#\$\%\&'\\*\+/=\?\^\_\`\{\|\}\~\-]+)\*@[a-Z0-9-]+(\.[a-Z0-9-]+)\*\.([a-Z]{2,})$"