Description:
------------
When a negative integer is passed as the $n_retries argument to imap_open(), the number is passed as a signed long to the c-client function mail_parameters(), which is expecting an unsigned long to be passed on a SET_MAXLOGINTRIALS call. This results in $n_retries being set to a huge number. The problem is the the function php_imap_do_open() in ext/imap/php_imap.c. 
Below is a patch written by Andy Wharmby (CVS ID wharmby), it returns a warning if $n_retries is less than 0:
The code as it stands is: 

#ifdef SET_MAXLOGINTRIALS
	if (myargc == 5) {
		convert_to_long_ex(retries);
		mail_parameters(NIL, SET_MAXLOGINTRIALS, (void *) Z_LVAL_PP(retries));
	}
#endif

SOLUTION:


#ifdef SET_MAXLOGINTRIALS
	if (myargc == 5) {
		convert_to_long_ex(retries);

		if (retries < 1) { 
			php_error_docref(NULL TSRMLS_CC, E_WARNING ,"Retries cannot be less than 1");
 			RETURN_FALSE;
		} 

		mail_parameters(NIL, SET_MAXLOGINTRIALS, (void *) Z_LVAL_PP(retries));
	}
#endif

The documentation for the $n_retries argument also says that the number passed is "Number of maximum connect attempts" which is incorrect. There is always one attempt to connect, if that fails then $n_retries sets how many more attempts are made *after* the initial attempt.

Reproduce code:
---------------
<?php
var_dump(imap_open($mailbox, $username, $password, null, -1));
?>