diff --git a/INSTALL b/INSTALL
index e98a62350..54d4eee9a 100644
--- a/INSTALL
+++ b/INSTALL
@@ -279,3 +279,8 @@ KNOWN ISSUES
 
 Installations with uw-imap server should set imap_disabled_caps = array('ESEARCH')
 in main configuration file. ESEARCH implementation in this server is broken (#1489184).
+
+PHP >= 5.6 validates the ssl certificates by default. It means that
+if IMAP/SMTP certificates are self-signed or use wrong host name you'll get
+connection errors. A solution in such cases is to set imap_conn_options,
+smtp_conn_options and managesieve_conn_options in a way described in config/defaults.inc.php.