If you cannot use LOAD DATA INFILE, your problem is that file_get_contents reads the whole big fat file into a single string. Don't.
If at all feasible, use fgets (http://www.php.net/manual/en/function.fgets.php)
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Explain concepts important to validation of email addresses with regular expressions. Applies to most languages/tools that uses regular expressions.
Consider email address RFCs:
Look at HTML5 form input element (with type=email) regex pattern: