no it is not illegal but is good to check first
No. This is done all the time by creditors.
Yes, it is illegal to open someone else's mail that is delivered to your address. This is a violation of federal law under the Mail Theft Statute.
Without permission-yes.
Yes, it is illegal to open a package that is addressed to someone else without their permission.
No, it is illegal to open mail that is addressed to someone else, even if it is sent to your address.
Ordering pizza to someone's house is not illegal. It is a common practice for food delivery services to deliver food to a specified address.
Yes, it is illegal for someone to use your email address without permission to sign up for things. This is considered identity theft and can be prosecuted under various laws.
Yes, but it's the post office you are supposed to give a fowarding address to.
The person not changing their address is not illegal; however, you tampering with someone else's mail most certainly is. I suggest you contact the post office and explain that you wish they no longer send you the individual's mail.
It is not illegal to post date a check. Though it is illegal in some states to request someone to write you a (or many) post dated checks to guarantee payment. The check is not legal tender until the date on the check.
Yes, it is illegal for someone to use your name and address to order things without your consent. This is a form of identity theft and can be considered fraud. If you suspect someone has done this, it is important to report the incident to the authorities.