hide calendar

[auiensrt]

Hi everybody,
I wanted to install an email-client, but it is an email-client with calendar on the right side. Please, how can I get rid of it or hide it?

[auiensrt]

I had to clik on "disable" down on the right.

[BlueSnow]

You can also Disable or Remove it under Tools>Add-ons. Lightning is the calendar.