SQL Duplicate Values After Transformation

Apex Systems QA engineers are validating imported contact records. Some email addresses differ only by capitalization or accidental surrounding spaces, which can create duplicate accounts in an internal QA data set.

Write a PostgreSQL query to identify duplicate email values after applying the transformation LOWER(TRIM(external_email)).

Requirements

1. Normalize each email by trimming surrounding whitespace and converting it to lowercase.
2. Return only non-empty normalized values that occur more than once.
3. Return the normalized email and its duplicate count, ordered alphabetically by the normalized email.