In a double opt-in list, all email address must be confirmed before they are added in mailing list. A request for confirmation is sent to the submitted address and the address owner must take actions to confirm below things:
1) Subscriber is the owner of email address.
2) The email address is working.
3) Subscriber want to join Newsletters.
To know more about Double opt in list, please refer our knowledge-base article here :- https://manage.accuwebhosting.com/kn...mail-list.html
Safe lists :
A safelist is a group of people who have agreed to receive emails from each other. Usually, the group requires membership and has rules regarding how often you are allowed to email the members.