Mailing lists, what do I do with them?

Hello,
So I could use some help and advice

I have come in to possession of some mailing lists and would like some ideas as to what to do with them.
Since I myself am new to all this I'm open to suggestions and ideas also glad to hear from you guys by pm's.

It all depends the niche and the audience.
Try some remarketing, sending to some similar niche website.