Direct answer
Select the contact range, open Data > Data cleanup > Remove duplicates and choose the email column. Make a duplicate sheet first and retain all columns in the selection.
More questions and answers
Can Google Sheets verify real email addresses?
A Sheets formula can validate a simple address pattern, but it cannot establish that an inbox exists. Export a CSV and use an email verification service for additional checks.
Why does TRIM leave weird spaces in my email sheet?
Some invisible characters, including nonbreaking spaces, survive ordinary trimming. Use a helper formula to replace the character, inspect the results, and preserve the untouched original.
How do I filter Gmail addresses from a Google Sheet?
Filter a helper column containing the domain after the @ symbol. A Gmail address is not automatically invalid or risky; filter it only for a legitimate segmentation need.
How do I merge verification results with Google Sheets contacts?
Use a stable key and a lookup to bring status, reason and checked date back beside each contact. Do not rely on the verifier preserving the same sort order.
Can I clean email addresses in Sheets without deleting unsubscribers?
Keep a suppression column and filter unsubscribed contacts out of sending exports. Verification does not override an opt-out and should never reset subscription status.
How do I remove case-only duplicate emails in Google Sheets?
The built-in duplicate tool can treat differently capitalised values as repeats. If combining exports, also trim hidden spaces and compare a normalised helper column.