Use official port name: imap not imap4.
 [rsc] --rw-rw-r-- M 330753 glenda sys 16258 Nov 27 22:19 sys/src/cmd/upas/fs/imap4.c
	/n/sourcesdump/2005/1127/plan9/sys/src/cmd/upas/fs/imap4.c:431,437 - 
	/n/sourcesdump/2005/1128/plan9/sys/src/cmd/upas/fs/imap4.c:431,437
	  	if(imap->mustssl)
	  		port = "imaps";
	  	else
	- 		port = "imap4";
	+ 		port = "imap";
	  
	  	if((imap->fd = dial(netmkaddr(imap->host, "net", port), 0, 0, 0)) < 0)
	  		return geterrstr();