SSL always on means there is no account transfer without forcing customers to change mailservernames.
Since even if you buy a (wildcard) cert for your customers domain name, they have to connect via the hostserver names to the services like exim, courier or dovecot. I don't a proxy solution to help migration. I don't see a way to use the hostname of the old server on a new server.
Since even if you buy a (wildcard) cert for your customers domain name, they have to connect via the hostserver names to the services like exim, courier or dovecot. I don't a proxy solution to help migration. I don't see a way to use the hostname of the old server on a new server.