If the valid-for-your-purpose set of domains is not huge you could use something like:

if ($mail_id =~ /\A(box1|box2|box3|other1|other2)*\.(yourcompany|other
+company|elsewhere)\.com\z/ ) {
  print "matched\n";
}
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If you want to ensure that non-existant combinations don't occur, then:

if ($mail_id =~ /\A(box1\.yourcompany\.com|box2\.yourcompany\.com|box3
+\.yourcompany\.com|other1\.othercompany\.com|other2\.elsewhere\.com)\
+z/ ) {
  print "matched\n";
}
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