[Tim]

PHP solution:

$subject = "to [Login 1] to [Login 2] to [Login 3] to [Login 4] произвольный текст";

# Логины
preg_match_all('/(to \[([^]]+)\])+/', $subject, $matches);

foreach($matches[2] as $key => $val) print "<br>$val";


# Произвольный текст
preg_match_all('/\]([^]]*$)/', $subject, $matches);

print "<br>".$matches[1][0];


Результат:
Login 1
Login 2
Login 3
Login 4
произвольный текст