How to Verify an Email List in Excel or CSV

Most contact lists start life in a spreadsheet. Excel is fine for sorting, filtering, and keeping an ID next to each address. It cannot query the receiving host about whether that inbox is still live. That step needs an email verifier, and the usual way to hand the data over is a CSV file. When you verify an email list in CSV form, you export from Excel or your CRM, upload the file, then merge the result columns back onto the original sheet.

This tutorial stays with the file itself: how to export a clean sheet, how to save it so a verifier can read it, and how to bring results back into Excel. Use the labels you actually see after you download the report. For deciding what each label means for the send, see the verification report guide.

The wider cleaning sequence (export, run, suppress, send) lives in the bulk verification walkthrough. After you have results, a later guide covers how to remove invalid rows.

Why Excel formulas are not enough

A spreadsheet can test whether a cell contains an @, whether the domain looks like a domain, or whether the same address appears twice. Those tests catch empty cells and some typos. They cannot see a mailbox that was closed last year, a domain that publishes no MX, or a temporary inbox created for one signup.

Mailbox-level verification talks to the destination the way a sending server would, without delivering a message. That work happens outside Excel. Your job in the workbook is to give the verifier a readable file and to have a key that lets you match every result to the original row.

Step 1: Export only the rows you plan to check

Start from the system that owns the list (your store, CRM, help desk, or last campaign export), not from a leftover desktop file whose age you cannot explain.

Filter to the segment you will actually mail or import, not the entire history of the company.
Include the email address and a stable identifier you already use (a contact ID, order ID, or CRM key).
Add any column you need later for permission (signup source, date, or list name) in your working copy. The verifier will not judge permission, but you will.
Write the source system name and the export date on the file itself so a later review can see where the sheet came from.

If two systems both hold “the” list, export each one separately and keep the source in a column. Mixing them first makes it harder to see which tool introduced a bad row.

Step 2: Make the workbook verifier-friendly

CSV is a single table. Before you save:

Keep one address per row. Split cells that contain two addresses separated by a comma or semicolon.
Put a clear header on the email column, such as email. Do not hide the header in row 3 under a title banner.
Convert formulas to values. A verifier reads what is stored in the file, not the Excel formula bar.
Use one worksheet. Extra sheets disappear when you save as CSV.
Remove totals, charts, pivot caches, and blank rows at the bottom that Excel still treats as part of the used range.
Drop columns you do not need for matching or permission. Extra personal data does not help the check and widens the spreadsheet you plan to submit.

Watch for Excel habits that quietly destroy addresses:

Scientific notation on numeric IDs (1.23E+15), which you will need intact when you merge results
Spaces at the start of a cell, copied from a web form
Line breaks inside a cell
“Smart” quotes pasted from an email
Locales that use a semicolon as the list separator, so a comma-separated file opens as one giant column

If your regional settings expect semicolons, save with a delimiter you can document, or export through a path that lets you choose UTF-8 and a comma. Consistency matters more than which valid delimiter you pick, as long as the verifier and Excel agree. If you work in Google Sheets instead of Excel, download a CSV from File, Download, and treat that file with the same rules: one sheet of values, one header row, and no second download-and-reopen loop that recasts your IDs.

Step 3: Save a CSV copy and keep the workbook

In Excel, use Save As and pick a CSV option that preserves Unicode characters when your list includes names or addresses outside basic English. A common choice on current Excel builds is CSV UTF-8. Give the CSV a name that includes the date and the segment (newsletter-active-2026-11-06.csv) and leave the original .xlsx untouched as your working book.

Open the CSV once in a plain text editor if you can, just to confirm that headers sit on the first line and that addresses were not wrapped in unexpected quotes. Then close it. Repeatedly opening a CSV in Excel and saving again is how IDs turn into scientific notation.

Store both files in the same folder. You will merge results back into the workbook, not into a second mystery export. If anyone else on the team might open the CSV, leave a one-line readme next to it that says “import as text, do not double-click.”

Step 4: Upload the file for verification

kukudze takes an uploaded CSV or TXT file, or a pasted list. That is the path this tutorial assumes. Sign up and confirm your email before the first check. Match the number of rows to your plan on the pricing page so a large export does not run out of checks halfway.

The Free plan gives 100 checks a month and takes lists up to 50 rows, which is enough to practice the file path on a sample. It runs the same 4 checks as every paid plan: format, domain, mailbox answer and accept-all. Do not invent a required column order; follow whatever the upload screen asks for when you get there. If the screen lets you mark which column holds the address, choose the header you created in Step 2.

Upload the CSV, not a screenshot and not a PDF printout of the sheet. Wait until the job finishes before you download anything. A partial file looks like a complete report and will not match row counts later.

Step 5: Bring the results back into Excel

Download the report the product gives you and open it with Excel’s import-from-text or data-from-CSV path so you can set the email and ID columns as text. Double-clicking the file often reapplies the same type-guessing that broke IDs on the way out.

Match results to your original workbook on the identifier you exported, or on the email address if that is the only key you have. Excel’s lookup functions (XLOOKUP or an index match) work well when both sides use the same text format. If one side has trailing spaces and the other does not, trim both before you match.

You may see more than one status-like column. Read the header row you received and record, in your own notes, which column you treated as the main status and which columns you treated as extra flags. A later glossary of verification result meanings will help you interpret common labels such as valid, invalid, unknown, and risky, even when vendors name them slightly differently.

Count rows. The number of results should line up with the number of addresses you uploaded, aside from duplicates the tool skipped. If the counts differ by more than that, stop and find the missing key before you suppress anything.

Step 6: Filter, decide, and save a sendable sheet

Create a working view rather than deleting rows from the only copy you have.

Keep a full archive sheet with every original row plus the result columns
Filter a sendable sheet to the rows your written rule allows
Move rejected rows to a suppression sheet so you can see what you dropped and why

A typical first rule is to exclude addresses the report marks invalid or otherwise undeliverable, then decide separately about rows the report marks unknown, accept-all, disposable, or role-based. Those extra flags, when they appear, are not the same as “does not exist.” Apply the policy you already use for campaigns, not a one-off guess.

Save the sendable sheet as its own CSV for the importing step, again as values, with the same care about encoding and IDs.

Step 7: Load the clean file back into the sending tool

Import only the sendable CSV into your email platform or store. Do not paste from the screen, which can split columns. After the import, spot-check a handful of addresses against the workbook so a delimiter problem did not shift every field by one column.

Then send, or schedule, only after that check. The spreadsheet work is finished when the sending tool and the workbook agree on who is still eligible.

A short checklist before you upload

One email per row and a header the import can read
A merge key that still exists in the original workbook
Formulas converted to values
CSV saved without reopening it a dozen times in Excel
Row count written down so you can compare it to the report
A written rule for invalid, unknown, and flagged rows
An archive copy you will not overwrite

FAQ

Can I verify addresses with an Excel formula alone?

No. Formulas can test shape and find duplicates. They cannot confirm that a mailbox accepts mail. For that you still upload to a verifier.

Should I upload the .xlsx file or a CSV?

kukudze takes CSV or TXT files, not .xlsx. Save a simple CSV with one sheet and clear headers for the upload. Keep the .xlsx as your working book.

What if Excel keeps changing long IDs?

Import the results using a text/CSV path and set the ID column to text. In the original workbook, format that column as text before you export. Avoid opening the CSV in Excel and saving it again unless you are sure the types stayed put.

What columns will the download contain?

Use the header row in the file you receive, and keep your own note of which columns you relied on.

How many rows can I check at once?

That depends on your plan on the pricing page. Free takes lists up to 50 rows and 100 checks a month. Split a file that would exceed the plan you are on, and run the parts as separate jobs so you can still match each report.

Wrapping up

Excel holds the list. A verifier judges the addresses. CSV is the envelope between them. If you export a tidy sheet, save it once as UTF-8, upload it, and merge results on a key you already trust, the round trip stays simple.

Begin the upload on the kukudze product page. Check each plan’s monthly cap under pricing so a file larger than your allowance does not stall halfway.