BoltMail
How can I let my contacts modify the details of their subscription?
To allow users to modify the details of their subscription, simply add a "Modify Details" link to your newsletter. You do this by selecting "Insert Custom Field" and adding the field titled "Modify Details". This will generate a link in your newsletter, pointing to a dynamically generated page, allowing your contacts to modify their own details.

The Modify Details custom field is created by creating a Website Form of the type Modify Details.