1 calendar for multiple mailboxes

Is it possible to view all calendar entries of various emails into one single calendar view? Example meetings, and reminders of multiple client mailboxes into one single calendar to avoid going into every separate client email.

Yes. eM Client offers a unified view of all calendars. Just add your calendar accounts in Menu > Tools > Accounts, then click on the + icon.

With some email accounts like Google, Outlook.com, GMX etc, the calendar and contacts will be added automatically when you add the email account, but for others (or if you just want the calendar and not the email) use the above option.

in the direct calendar view the subscribed calendars are listed on the left side. With a check mark they can be displayed in the calendar -> all calendars are ticked all are visible in this view.

But they are still showing as separate calendars. Is there the function to merge all calendars into one calendar?

Yes, because they are separate calendars. If you want just one calendar, move the events from all your calendars into one calendar, then remove the other calendar accounts from eM Client.

Either you have one calendar, or you have may calendars. You choose.

Fortunately it does not matter if you have many calendars because eM Client will display them in a single unified view, with each calendar’s events in a separate color. If you don’t like the separate colors, right-click on each calendar name and choose Calendar Color. Then make them all the same color.

The unified view is a much better option than moving all your events to a single calendar, especially if you decide you don’t want to see all the calendars at one time. Those you don’t want to see, just untick them.

In the above example, the second and third in the list will not be displayed in the calendar. When you want to include them again, just tick their boxes.