I have zimbra email server that perfectly running on an other server. Now we want to integrate zimbra emails to our nextcloud server so that users of nextcloud can access their emails from nextcloud server, they do not need to login zimbra server separately. Users that are available in NC should use same credentials for zimbra emails.
I don’t know Zimbra. But if you can connect to it via IMAP and SMTP it should work. Nextcloud Mail acts as any other (desktop) IMAP / SMTP mail client.
In theory it should be possible to use the Nextcloud LDAP application to authenticate your Nextcloud users against the the Zimbra LDAP service…