How to check email columns before import

Step-by-step approach

Identify the exact email column and ensure its header is present.
Use the CSV Email Validator to detect obvious syntax problems.
Review rejected entries for spaces, missing @ symbols and mistaken separators.
Correct the source records using verified information rather than inventing addresses.
Remember that format validation cannot prove an inbox exists or accepts messages.

Try the matching tool

Open Email Validator to work on a local copy. Review the result before importing it elsewhere.

What this does not solve

Browser tools can validate known structures and transform available data, but cannot restore deleted or corrupted bytes, infer unknown business facts, or guarantee that a target system will import every field as intended.