As I wrote earlier, you can disable the use of IPv6 in Mailcow. Of course, you will then not be able to receive emails from or send emails to IPv6-only mail servers.
If you manage your server yourself, however, you must also be able to install operating system updates and adjust other settings (such as the network configuration) yourself. If you don’t know how to do this, sooner or later you will have problems anyway and may not be able to fix errors in your installation on your own.
