Description:
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Per RFC 3501 [9], spaces are valid characters in a username.  Thus, 'username' != ' username '.  However, imap_open() appears to be stripping leading/trailing whitespace from the username.

Test script:
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<?php

$mailbox = '{localhost:143}INBOX';
// 'username' is valid user; ' username ' is invalid user
$username = ' username ';
$password = 'password';

$res = imap_open($mailbox, $username, $password, OP_HALFOPEN);

if (is_resource($res)) {
    print "SUCCESS\n";
} else {
    print "FAILED\n";
}


Expected result:
----------------
FAILED

Actual result:
--------------
SUCCESS