IMAP Client auth issue

Hi All.

I cannot get IMAP Mail Clients - eg Thunderbird and Outlook - to authenticate to the server. They just show an error:
mail dovecot: imap-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=192.168.1.2, lip=192.168.1.253, TLS, session=
They find the server and its settings correctly but fail to complete with the above error (from the /var/log/imap log) each time they try.

It is a clean install with just the Active Directory setup and the mail server and horde installed;
Horde works perfectly. I also tried running webtob and sogo and they also work perfectly via their webclient.

It is a standalone server without gateway.

I have tried connecting the client using IP addresses and domain name on the LAN and WAN;
It is a FQDN with correct routing and SSL installed.
Tried ‘username’ and ‘username’@‘domain’ all with the same result;

Any suggestions as to what I may be missing? The logs suggest the connection is correct, the clients suggest the username or password is incorrect (checked and double-checked).

Thanks.
Klaus

NethServer Version: NethServer release 7.6.1810 (final)
Module: nethserver-mail-server

Is there any antivirus installed on the client, filtering email protocols?

Thanks for the suggestion Michael, but no. Connectivity and activity looks right by the logs.

Klaus

I’ve had some success with this. Thunderbird connected by turning off connection security (TLS etc). Outlook is no longer that configurable.

Will play and check conf at the server end to make the process simpler and report back in.

Klaus

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Certificate is self-signed or Let’sencrypt provided?

LetsEncrypt Michael, yet I’m going to uninstall/reinstall again as I may not have selected that as the default server cert (assuming it would just do so :frowning: )