$re = '/(?:^|\r?\n)(.*?)(?: |\r?\n)([^\s]+?@.*?)(?=\r?\n|$)/';
$str = 'Vicente Clark vicente.clark@gmail.com
Mark van der Zant
mark.zant@protonmail.com
Georgy Collins
georgy.collins@yahoo.com
Paul Danilsson
paul.danilsson@live.com';
$subst = "$1: $2\n\n";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php