Sorry, but your problem does not imply a bug in PHP itself.  For a
list of more appropriate places to ask for help using PHP, please
visit http://www.php.net/support.php as this bug system is not the
appropriate forum for asking support questions. 

Thank you for your interest in PHP.

Why not a bug? why bogus? 
Please look at sendmail.c in win32 directory:
	if (headers && (pos1 = strstr(headers, "Cc:"))) {
		if (NULL == (pos2 = strstr(pos1, "\r\n"))) {
			tempMailTo = estrndup(pos1, strlen(pos1));
		} else {
			tempMailTo = estrndup(pos1, pos2-pos1);
		}

		token = strtok(tempMailTo, ",");
		while(token != NULL)
		{
			sprintf(Buffer, "RCPT TO:<%s>\r\n", token);
			if ((res = Post(Buffer)) != SUCCESS)
				return (res);
			if ((res = Ack()) != SUCCESS)
				return (res);
			token = strtok(NULL, ",");
		}
		efree(tempMailTo);
	}

in this code, we can see, what in Buffer posts line like:
RCPT TO: <Cc: email@address.org> for first Cc: address and right string for (RCPT TO: <secondaddress@dot.com>)

it is really strange?

Right code:
if (headers && (pos1 = strstr(headers, "Cc:"))) {
                pos1+=3;
		if (NULL == (pos2 = strstr(pos1, "\r\n")))
......
after this procedure add:
pos1-=3;

Please try using this CVS snapshot:

  http://snaps.php.net/php4-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php4-win32-latest.zip

This bug has been fixed in CVS.

In case this was a PHP problem, snapshots of the sources are packaged
every three hours; this change will be in the next snapshot. You can
grab the snapshot at http://snaps.php.net/.
 
In case this was a documentation problem, the fix will show up soon at
http://www.php.net/manual/.

In case this was a PHP.net website problem, the change will show
up on the PHP.net site and on the mirror sites in short time.
 
Thank you for the report, and for helping us make PHP better.

Vladimir:
  This is fixed correctly in sendmail.c:1.32. See http://cvs.php.net/co.php/php4/win32/sendmail.c?login=2&r=1.32 for fix.

-- Joey