Address no longer valid notice

I got a message saying "Address no longer valid See https://helpdesk.it.helsinki.fi/help/10555"

The e-mail address of your intended recipient is no longer in use as of 5 June 2017. If the user has not set up another e-mail account, the messages will no longer be sent. Please contact the owner of the e-mail address in some other way.

The e-mail address is mine

If you want to take this e-mail address back into use, then please install and activate Office 365.