dl("imap4r2.dll");
 #mbox = imap_open("{wins21.com}INBOX", $login, $pass);

  is not work correctly.

  > Couldn't open stream....  

  other dll library required ?

 ==========================================
  In WindowsNT (define WIN32)

  mail_link($mbxdriver) is twice defined.
 ==========================================

 I was found that ...

 ================== function/imap.c ===============
222 int imap_init(INIT_FUNC_ARGS)
223 {
224 #if WIN32|WINNT
225	mail_link (&mbxdriver);      /* link in the mbox driver */  <----------- defined
226 #else
227	mail_link(&unixdriver);   /* link in the unix driver */
228 #endif
229	mail_link (&imapdriver);      /* link in the imap driver */
230	mail_link (&nntpdriver);      /* link in the nntp driver */
231	mail_link (&pop3driver);      /* link in the pop3 driver */
232 #if !(WIN32|WINNT)
233	mail_link (&mhdriver);        /* link in the mh driver */
234	mail_link (&mxdriver);        /* link in the mx driver */
235 #endif
236	mail_link (&mbxdriver);       /* link in the mbx driver */  <---- too defined !!!!!!!!
237	mail_link (&tenexdriver);     /* link in the tenex driver */
238	mail_link (&mtxdriver);       /* link in the mtx driver */

 225, 236 line, mail_link($mbxdriver) is twice defined.

  delete 225 line, and MUST Compile php source.