Place display ads specifically for inactive subscribers. Facebook or Google AdWords offer corresponding possibilities. Important: A corresponding opt-in of the contacts must of course be available.
Vary the sending time significantly, for example from Tuesday morning to Thursday afternoon. For each recipient, there are times when they are regularly out of the office or otherwise busy.
Some subscribers may like your offer – but not in too high a dose. Allow them to receive your newsletter at a lower delivery frequency in the future. It’s hard to believe, but this trick sometimes works wonders.
With sophisticated campaigns, you can easily reactivate 10% of all “cold” contacts. Lead magnets, competitions, incentives, or surveys are helpful here. In each case, followed by a deadline by which a subscriber should please reactivate their subscription in order not to be deleted from the distribution list.
If possible within the scope of the opt-in, also use other channels to make contact. Especially in a personal conversation, it is easy to find out how interested the subscriber is.
Reactivation of thousands of e-mail addresses is difficult in principle if you do not know the exact cause of inactivity. Therefore, in the vast majority of cases, you will be unsuccessful. Therefore, do not set your expectations too high. Identify possible reasons as best you can and take them into account in your campaigns.