You have the option of integrating your mail.ch calendars into external calendar programs. In this way you can keep your calendar up to date, even if you manage it on different devices with different programmes. The CalDAV protocol is used for this purpose. If a calendar software supports the CalDAV protocol, you can integrate and synchronise the mail.ch calendar there.
Unfortunately, the CalDAV standard is not supported by all calendar programs, as these have either implemented their own proprietary solution (Microsoft Outlook), or have not (yet) integrated a solution for integrating external calendars (Calendar in Android). Sometimes it helps to install plug-ins or external apps that enable the CalDAV standard.
Another way to access your calendars is the ICS export. Some programmes such as Apple Calendar or Microsoft Outlook (from 2007) support a subscription function. There, the URL of a calendar and the user name + password must be entered, and then the calendar can be accessed for reading. The calendar is then also regularly re-downloaded and kept up to date. The URL looks like this:
The parameter ?export is important. You can find out exactly what the URL for your calendars is in the settings mode, under Calendar -> Internal Calendar Names.