The Collection Actions package of utility actions now has a new action that takes a collection of recordIds (i.e. a List of Strings) and returns the corresponding records. It carries out a SOQL query and obtains the fields that you specify by name.
In this example, I start out with a collection of AccountTeamMembers to whom I want to send emails. To get their email addresses, I need to obtain the User records that correspond to each AccountTeamMember. I can do that by pairing these two actions:
The first action is Extract Strings from Collections, which is also available in the Collection Actions package. I use this to convert the AccountTeamMembers into a List of User Ids. Then I ‘hydrate’ the User Ids into User records.
Install Collection Actions here.