Is there any benefit to marketing the unsubscribed contacts to see if they want to resubscribe? In my business, which is advertising real estate agents' properties, if the agent forwards one of their email flyers that advertises a property to a client, and that client is not interested in the property, the client is able to click the unsubscribe button at the bottom which unsubscribes the agent - and the agent doesn't even know they're being unsubscribed! So, I'm wondering if some of my agents are unsubscribed through no fault of their own and would like to be included again in my list. Has anyone marketed to unsubscribed contacts?
Legally and technically speaking, we don't ever recommend trying to reach out to unsubscribed contacts. If your concern is that contacts are being unsubscribed because they're forwarding emails to other people who then unsubscribe them (keep in mind that these forwardees have to also explicitly confirm the email address being unsubscribed), then you'll likely want to encourage your contacts to not forward your emails. There's other ways they can share your emails, such as via social media or through the View as Webpage link.
For more details on what you can include in your email to make sharing it better, I'd advise going through these articles: