Patch taken from http://bugs.php.net/bug.php?id=42862 as this still isn't fixed in HEAD
--- ext/imap/php_imap.c.orig	2007-07-31 01:31:10.000000000 +0100
+++ ext/imap/php_imap.c	2008-03-04 17:48:30.000000000 +0000
@@ -70,6 +70,7 @@
 static void _php_imap_add_body(zval *arg, BODY *body TSRMLS_DC);
 static void _php_imap_parse_address(ADDRESS *addresslist, char **fulladdress, zval *paddress TSRMLS_DC);
 static int _php_imap_address_size(ADDRESS *addresslist);
+static void _php_rfc822_write_address_len (char *dest, ADDRESS *adr, int len);
 
 /* the gets we use */
 static char *php_mail_gets(readfn_t f, void *stream, unsigned long size, GETS_DATA *md);
@@ -2137,7 +2138,7 @@
 	}
 
 	string[0]='\0';
-	rfc822_write_address(string, addr);
+	_php_rfc822_write_address_len(string, addr, sizeof(string));
 	RETVAL_STRING(string, 1);
 }
 /* }}} */
@@ -2906,13 +2907,13 @@
 				if (env->from && _php_imap_address_size(env->from) < MAILTMPLEN) {
 					env->from->next=NULL;
 					address[0] = '\0';
-					rfc822_write_address(address, env->from);
+					_php_rfc822_write_address_len(address, env->from, sizeof(address));
 					add_property_string(myoverview, "from", address, 1);
 				}
 				if (env->to && _php_imap_address_size(env->to) < MAILTMPLEN) {
 					env->to->next = NULL;
 					address[0] = '\0';
-					rfc822_write_address(address, env->to);
+					_php_rfc822_write_address_len(address, env->to, sizeof(address));
 					add_property_string(myoverview, "to", address, 1);
 				}
 				if (env->date) {
@@ -3883,6 +3884,34 @@
 /* }}} */
 
 
+/* {{{ _php_rfc822_soutr
+ */
+static long _php_rfc822_soutr (void *stream,char *string)
+{
+	return NIL;
+}
+
+/* }}} */
+
+
+/* {{{ _php_rfc822_write_address_len
+ */
+static void _php_rfc822_write_address_len ( char *dest, ADDRESS *adr, int len)
+{
+	RFC822BUFFER buf;
+
+	buf.beg = dest;
+	buf.cur = buf.beg;
+	buf.end = buf.beg + len - 1;
+	buf.s = NIL;
+	buf.f = _php_rfc822_soutr;
+	rfc822_output_address_list (&buf, adr, 0, NIL);
+	*buf.cur = '\0';
+}
+	
+/* }}} */
+
+
 /* {{{ _php_imap_parse_address
  */
 static void _php_imap_parse_address (ADDRESS *addresslist, char **fulladdress, zval *paddress TSRMLS_DC)
@@ -3897,7 +3926,7 @@
 	if ((len = _php_imap_address_size(addresstmp))) {
 		tmpstr = (char *) pemalloc(len + 1, 1);
 		tmpstr[0] = '\0';
-		rfc822_write_address(tmpstr, addresstmp);
+		_php_rfc822_write_address_len(tmpstr, addresstmp, len);
 		*fulladdress = tmpstr;
 	} else {
 		*fulladdress = NULL;