使用你展示的例子，请尝试下面的正则表达式。这里是使用正则表达式的Online Demo。

^(?:[0-9]*\s*[pP](?:\.O\.|o)(?:st(?:al)?\soffice\s)*[bB]ox(?:\sstreet)?)$

***说明：***添加上述正则表达式的详细说明。

^(?:                 ##Starting 1 non-capturing group from starting of the value.
  [0-9]*\s*          ##Matching 0 or more digits followed by 0 or more spaces.
  [pP]               ##Matching p OR P here.
  (?:\.O\.|o)        ##In a non-capturing group matching .O. OR o here.
  (?:st(?:al)?\soffice\s)*  ##In a non-capturing group matching st followed by spaces followed by office followed by spaces and keeping this non-capturing group Optional.
  [bB]ox             ##Matching b OR B followed by ox here.
  (?:\sstreet)?      ##In a non-capturing group matching space street and keep this optional.
)$                   ##Closing non-capturing group at the end of the value here.

下面是另一个适合您的变体：

/^(?:\d+\s*)?p\.?o\.?(?:st(?:al)?)?(?:\s+office)?\s*b(?:ox|in)\b.*/gmi

RegEx Demo
因为我们在这里使用忽略大小写修饰符，所以我们可以在正则表达式中使用所有小写字母。