Error with Z-Push BackendIMAP->Logon()

Hi,
I have a problem with Z-Push, my clients sometime received a pop-up on outlook and require login. After I checked the z-push log, i see that, and how I can fix it ? Thanks in advance !

23/10/2016 11:55:35 [15818] [ERROR] [client@domain.com] BackendIMAP->Logon(): can’t connect as user ‘client@domain.com’ on ‘{127.0.0.1:993/imap/ssl/norsh/novalidate-cert}’: [CLOSED] IMAP connection broken (server response)
23/10/2016 11:55:41 [10279] [ERROR] [client@domain.com] BackendIMAP->Logon(): can’t connect as user ‘client@domain.com’ on ‘{127.0.0.1:993/imap/ssl/norsh/novalidate-cert}’: [CLOSED] IMAP connection broken (server response)
23/10/2016 11:55:49 [15818] [ERROR] [client@domain.com] BackendIMAP->Logon(): can’t connect as user ‘client@domain.com’ on ‘{127.0.0.1:993/imap/ssl/norsh/novalidate-cert}’: [CLOSED] IMAP connection broken (server response)
23/10/2016 12:12:41 [21427] [ERROR] [client@domain.com] BackendIMAP->Logon(): can’t connect as user ‘client@domain.com’ on ‘{127.0.0.1:993/imap/ssl/norsh/novalidate-cert}’: [CLOSED] IMAP connection broken (server response)
23/10/2016 12:12:49 [21427] [ERROR] [client@domain.com] BackendIMAP->Logon(): can’t connect as user ‘client@domain.com’ on ‘{127.0.0.1:993/imap/ssl/norsh/novalidate-cert}’: [CLOSED] IMAP connection broken (server response)
23/10/2016 12:12:55 [21440] [ERROR] [client@domain.com] BackendIMAP->Logon(): can’t connect as user ‘client@domain.com’ on ‘{127.0.0.1:993/imap/ssl/norsh/novalidate-cert}’: [CLOSED] IMAP connection broken (server response)
23/10/2016 12:13:03 [21440] [ERROR] [client@domain.com] BackendIMAP->Logon(): can’t connect as user ‘client@domain.com’ on ‘{127.0.0.1:993/imap/ssl/norsh/novalidate-cert}’: [CLOSED] IMAP connection broken (server response)
23/10/2016 12:42:52 [26567] [ERROR] [client@domain.com] BackendIMAP->Logon(): can’t connect as user ‘client@domain.com’ on ‘{127.0.0.1:993/imap/ssl/norsh/novalidate-cert}’: [CLOSED] IMAP connection broken (server response)
23/10/2016 19:32:44 [29329] [ERROR] [client@domain.com] BackendIMAP->Logon(): can’t connect as user ‘client@domain.com’ on ‘{127.0.0.1:993/imap/ssl/norsh/novalidate-cert}’: [CLOSED] IMAP connection broken (server response)
23/10/2016 19:32:50 [29295] [ERROR] [client@domain.com] BackendIMAP->Logon(): can’t connect as user ‘client@domain.com’ on ‘{127.0.0.1:993/imap/ssl/norsh/novalidate-cert}’: [CLOSED] IMAP connection broken (server response)
23/10/2016 19:32:54 [ 3832] [ERROR] [client@domain.com] BackendIMAP->Logon(): can’t connect as user ‘client@domain.com’ on ‘{127.0.0.1:993/imap/ssl/norsh/novalidate-cert}’: [CLOSED] IMAP connection broken (server response)
23/10/2016 19:46:38 [ 6883] [ERROR] [client@domain.com] BackendIMAP->Logon(): can’t connect as user ‘client@domain.com’ on ‘{127.0.0.1:993/imap/ssl/norsh/novalidate-cert}’: [CLOSED] IMAP connection broken (server response)
23/10/2016 19:46:50 [ 7612] [ERROR] [client@domain.com] BackendIMAP->Logon(): can’t connect as user ‘client@domain.com’ on ‘{127.0.0.1:993/imap/ssl/norsh/novalidate-cert}’: [CLOSED] IMAP connection broken (server response)
23/10/2016 19:46:52 [ 7598] [ERROR] [client@domain.com] BackendIMAP->Logon(): can’t connect as user ‘client@domain.com’ on ‘{127.0.0.1:993/imap/ssl/norsh/novalidate-cert}’: [CLOSED] IMAP connection broken (server response)
23/10/2016 22:20:27 [ 7562] [ERROR] [client@domain.com] BackendCardDAV->Logon(): User ‘client@domain.com’ failed to authenticate on ‘https://127.0.0.1:443/carddav/addressbooks/client@domain.com/’:
23/10/2016 22:21:30 [ 6170] [ERROR] [client@domain.com] BackendCardDAV->Logon(): User ‘client@domain.com’ failed to authenticate on ‘https://127.0.0.1:443/carddav/addressbooks/client@domain.com/’:

You could check the status of the link with this command. See if there are any errors:

z-push-admin -a list -u client@domain.com