Hi ! I'm going to migrate ISPConfig 3 from Ubuntu 16 LTS to Debian 9 Stretch. During my previous migration I've got problem with mail server identification for e-mail client (Apple Mail). For whatever reason it recognized it is as new and loaded large number of old (already read messages) from pop mailboxes (we use Apple Mail on many desktops, so its a real problem). How to transfer e-mail server identification from ISPConfig 3 on Ubuntu 16 LTS to Debian 9 Stretch ? Is it enough to copy smtpd.key, smtpd.cert /etc/postfix -> /etc/dovecot, and fix permissions? Are there any other SSL certificates related to e-mail needed to copy? Thanks in advance.