Deleting mail users with CRM mail addon

Deleting mail users with CRM mail addon

I have 3 mail users who no longer work for our organisation therefore do not wish to pay subscription fees for these users. If these users are deleted, a warning appears indicating all mail will be deleted. Each of these users also had mail addon for the CRM. The users have been deactivated in the CRM and a backup has been created in the CRM.  If the mail users are deleted in ZOHO mail, is all mail deleted from the CRM even though a backup has been done?