<?php

$log = <<<FIM
##################################################
----------------------------------------
Nome: nome_user,
Email: email@user.com,
-------------------------------
,
----------------------------------------
##################################################
FIM;

    if( preg_match( '/Email:\s*(.*)\s*,/', $log, $matches ) ) {
        echo $matches[1];
    } else {
    	echo 'Não encontrado';
    }