Hello everyone, My client are not able to connect their outlook email client with my ispconfig (Roundcube intergration) server. The outlook shows invalid or expire certificate for the ispconfig server. However I have install letsencrypt certificate for my ispconfig GUI and it is validated by my brower. The clients have properly setup email domains, mail boxes and whenever they try to connect using outlook with following details they are greeted with the certification expire or invalid error of the host server: Incoming server: mail.client.com Username: client Password: Somepassword Port:993 Outgoing server:mail.client.com Username:client Password: somepassword Port:587 But when I entry my ispconfig servers URL (myispconfigserver.com) on the incoming and outgoing server the client is able to connect via outlook. But they are not able to connect via their domainYmail.client.com) hosted in my ispconfig server. The DNS record for client.com is also maintained with proper A records and so on The mail.client.com A record is pointed towards the ispconfig servers IP. The ispconfig mail.log shows outlook connecting to the ispconfig servers certificate and not the clients own certificate i.e mail.client.com certificate. Also i have installed my ispconfig servers lets encrypt certificate on the postfix and dovecot as well. May be that is the reason why i am getting certificate invalid or expire error. I think the error is due to the clients domain name and certificate mismatch. Can any one help me with the possible reasons and solution to it.