Hi Lynn,
To make it easy for customers, you can let them know that they can think of a customer journey as a campaign equivalent - basically that it can be short or long running, and have different activities/tasks/etc. associated to the campaign. The major differences of a customer journey versus a campaign are that you cannot use the rich email editor with a campaign/quick campaign nor can you obviously use segmentation for them either. Also as you know, a segment used in a customer journey must always come back to the contact in order for the segment to work correctly, which isn't the case for a marketing list. My general rule is if you need to just send something quick without fanfare and don't need insights on it, then a campaign/quick campaign is a good option. But if you are truly marketing to someone, you should be using the journeys, segmentation, rich email designer and taking advantage of the insights from your entities in Dynamics 365 for Marketing.
Hope this helps.
Megan
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