One can mailout to more than one List or Segment of a List in one mailout. When you do so the system creates a new Merged List which will have had any duplicate Email Addresses removed.
It is essential however that when mailing such a Merged List you set “Subscriber Actions” > “Actions when Unsubscribe” in List Setup of that Merged List to ALSO change the status of any Unsubscribes to “Unsubscribed” in the ORIGINAL Lists you merged, otherwise they will only be Unsubscribed from the Merged List. If you do not do that it will lead to Abuse Reports when you mail the original Lists again, from people who have Unsubscribed.
That does irreperable damage to YOUR online reputation with the Spam Filters.
Do NOT set Autoresponder Campaigns to go to Merged Lists as a Merged List is not Dynamic so new Subscribers are not added to a Merged List – they are added to the original Lists.
Selecting more than one List or Segment for a Mailout is done in Campaigns > Create new Campaign
Now create the Campaign and carry on to the “Confirmation” page as below. Set the time to be sent AT LEAST 30 minutes later than the current time to allow time to complete this sequence.
Now go to Lists and the Merged List will be displayed
Edit that List and scroll down to
Scroll down again to “Save” and any one who Unsubscribes will be Unsubscribed from both the Merged List AND the Original Lists.
If you use Multi List Broadcasts it is ESSENTIAL that you adhere to this bit of discipline otherwise you will do irreperable damage to YOUR online reputation as a “Sender” with the Spam Filters and there is NOTHING we (or you) can then do to repair that.