You can send your email campaign to multiple contact lists. You can select the contact lists in the list selection step of the email creation process.
In case a contact is listed on more than one list, that person will receive only one copy of the email. For e.g. email@example.com exists in your lists named "Summer List", "Winter List" and "Autumn List". You select all these lists for your email campaign. Now even though "firstname.lastname@example.org" is present in all the three lists, only one email will be sent to that email (instead of three).
We also automatically filter out unsubscribes from the lists.