This is not a simple issue.
Normally when you share your tree, you are sending the link to an individual in the tree and you want the tree to open up with that person selected.
Creating a mass email will make it necessary to pick someone on the tree to be the center of focus (the selected individual when the tree opens). This should be someone that does not have edit permissions (like yourself) as you don’t want everyone editing your tree. You can even choose someone that is not alive by temporarily editing the persons personal info by checking the “this person is alive” check box. (Family echo will not create a link to a dead person.)
Once you have selected the person, click on the [Share] button then make sure the “Allow Xxxx to edit family” option is unchecked. You can now copy the link at the bottom left of the window and use it in your mass mailing. Check the link first to make sure it works as you expect.