imap_search function is not fully compatible with IMAP4. the c-client used as of now supports only IMAP2 and some search criterion will not be available for use such as "OR"
So a php code similar to:
$inbox = imap_open('{imap.example.com:993/imap/ssl}INBOX', '[email protected]', 'pass123', OP_READONLY);
$search_string = 'SUBJECT "FedEx" OR SUBJECT "USPS"';
$emails = imap_search($inbox, $search_string);
will throw an error saying "Unknown search criterion"
observations and reference:
PHP source trace:(ref: https://github.com/php/php-src/blob/master/ext/imap/php_imap.c)
/ext/imap/php_imap.c -> line no : 4126
imap_search => line no : 4148
c-client library source trace:
src/c-client/mail.c -> line no : 3973
internal.txt -> line no : 1919 => mail_criteria()
criteria IMAP2-format search criteria string
WARNING: This function does not accept IMAP4 search criteria.
IMAP2 RFC1064 => [ref: https://tools.ietf.org/html/rfc1064] [page: 13]
IMAP4 RFC2060 => [ref: http://www.faqs.org/rfcs/rfc2060.html] [section: 6.4.4]
Note:
The core search functionality in a core module(IMAP) is still not available in PHP. Hope this will be brought to the developer community's attention...