When you "unsubscribe" a spam email as against a genuine company email all you are doing is alerting the spammer that they have a live email address and they then add that on to their list and this generates further spam email.
If it is spam or an unwanted email just mark it as spam and delete it. Do not click on any links or unsubscribe. If possible don't even open it because spammers can tell when an email is opened. There is a legal way of knowing that which you can read about by doing an Internet search.
There is no bulk way of deleting emails using webmail (using a web browser).
You could download and use an email client/app to access your email and this will allow bulk deleting.
If you want to delete multiple emails when using a web browser try the following.
If you hold down the shift key then tick the box to the left of the first email you want to delete in the list of emails then scroll down using the scroll bar on the right hand side and tick the last email you want to delete then release the shift key. It will select all the emails in between. You can then click delete or drag and drop them into the Trash folder.
There will be a limit of about two hundred emails per selection so depending on how many emails you have you may have to do this many times.
Once in the Trash folder you can empty that folder with one click.
Your email address can not be moved to a different service provider.
