If I understand correctly, you need to parse a string into a list. Ideally, there’d be a built-in dynamic expression operator to split a string using a user-defined string as the delimiter; but I don’t think that’s available yet in Bubble.
However, it can be done using a simple regular expression (regex). See the following demo…
The key is the regex which splits the multi-line input, minpEmailAddresses, on the newline character…
Once you have the list, use merged with to merge it with the user’s existing list that’s already in the DB so as to eliminate duplicates.
It’d be a good idea to also use the :trimmed and :lowercase operators for consistent formatting of the addresses.
-Steve