$re = '/(.+?:){3}(.*)/m';
$str = '"msg: Malware/Virus detected - Rtf.Exploit.CVE_2017_11882-6584355-0:Message denied for delivery:Announcement: Holiday Tomorrow"
"msg: Malware/Virus detected - Rtf.Exploit.CVE_2017_11882-6584355-0:Message denied for delivery:Announcement Holiday Tomorrow"
"msg: Malware/Virus detected - Rtf.Exploit.CVE_2017_11882-6584355-0:Message denied for delivery Announcement Holiday Tomorrow"
"msg: Malware/Virus detected - Rtf.Exploit.CVE_2017_11882-6584355-0:Message denied for delivery:Announcement: Holiday: Tomorrow"
"msg Malware/Virus detected - Rtf.Exploit.CVE_2017_11882-6584355-0:Message denied for delivery:Announcement: Holiday: Tomorrow"';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($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