How do I find invalid emails in an old mailing list?

A practical way is to combine quick cleanup checks with verification tools:

1) Remove obvious bad entries

Look for and delete addresses that are clearly invalid:

• Missing @
• Missing domain part: name@
• Missing local part: @domain.com
• Typos like gmail.con, yahooo.com
• Spaces or illegal characters
• Duplicate addresses

2) Run a basic format check

Use a simple email regex or a spreadsheet formula to flag entries that don’t match a standard email pattern.
This catches formatting problems, but not emails that are correctly formatted yet no longer exist.

3) Check domain validity

For each address:

• Verify the domain has valid MX records
• Flag domains that don’t exist anymore
• Watch for dead corporate domains if the list is old

4) Use an email verification service

Tools like these can test whether an address is likely deliverable:

• NeverBounce
• ZeroBounce
• BriteVerify
• Kickbox
• Hunter Email Verifier

These services typically classify emails as:

• Valid
• Invalid
• Catch-all
• Risky/unknown

5) Check for role-based or disposable emails

You may want to flag:

• info@, support@, admin@
• Temporary/disposable email domains

6) Clean in batches

For an old mailing list, don’t remove everything at once. Instead:

• Mark questionable addresses
• Test a small sample
• Compare bounce rates if you plan to send a re-engagement campaign

7) Best practice before sending

If this list is old, send a re-permission or reconfirmation email to active-seeming contacts and suppress anyone who doesn’t respond.

If you want, I can also help you with:

• a spreadsheet formula to flag invalid emails,
• a Python script to clean a CSV list,
• or a step-by-step workflow for Excel/Google Sheets.