If it's just one field from a given record, but for a group of records, you can use the List function.
If you can set up a relationship like this:
EmailTable::Field = RecordsForEmail::Field
Then a calculation field defined in EmailTable can use List ( RecordsForEmail::EmailBodyField )
To produce a return separated list of values from the related RecordsForEmail table. If you don't want them separated by returns, you can include a subsitute function:
Substitute ( List ( RecordsForEmail::EmailBodyField ) ; ¶ ; ", " )
If you can't set up such a relationship, you can use either a looping script or copy all records to get this same list of values from the current found set.