IMAP search by subject fails on punctuation characters on Gmail

I am using the PHP IMAP libraray's imap_search() function to search mails in a Gmail inbox via the subject string.

imap_seach($mbox, 'ALL SUBJECT "<search string>"');

This search returns perfectly fine for alphanumeric strings but fails when it has special characters like slash, comma, colon, single quote, hyphen, and many 开发者_如何学Pythonother characters that I do not even know of. Escaping them doesn't help. Replacing a few of them with space helps sometime but not in all cases.

Is there a standard way to filter the search string so that it never errors out and returns some result? I have tried tokenizing the subject sting and removing all words from the search string which even one alphanumeric characters. This mostly works but fails when all the words have non-alphanumeric character (which is common for single or two word subject).

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I'm guessing that GMail search goes by the idea that only whole alphanumeric words can be used as search strings..

Therefore you'd have to remove all non-alphanumerics from your search string, and it will work...