$re = '/Account For Which Logon Failed.* Account Name:.+?\b(.*?)\s/s';
$str = ' An account failed to log on.
Subject:
Security ID: S-1-5-21-1287344763-2688370722-3395302928-19873
Account Name: service_adfs
Account Domain: DOMAIN
Logon ID: 0xD62E4
Logon Type: 3
Account For Which Logon Failed:
Security ID: S-1-0-0
Account Name: user.thatiwant@DOMAIN.com
Account Domain: ';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($matches);
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