Verify Emails Before a Gmail Mail Merge (GMass, YAMM, Mailmeteor)

Verify the sheet before running a Gmail mail merge: export it as CSV, check every address, add the result back as a column, and filter the merge to valid addresses only. GMass, YAMM and Mailmeteor all send from your own Gmail or Workspace account, so every bounce and complaint lands on that account, not on a separate sending service.

Why mail merges need extra care

A mail merge feels like sending normal email, but at volume. That brings risks:

Risk	Why it matters for a mail merge
Bounces	Count against your own account's reputation
Daily limits	Hitting them can block sending for up to 24 hours, including your normal mail
Complaints	Affect the account you use for everything else
Shared domain	On Workspace, problems can affect colleagues on the same domain

Google publishes daily limits of 500 recipients for personal Gmail and 2,000 messages per user for Workspace; mail merge tools may apply lower caps. Our Gmail sending limits guide explains the details.

Step 1: Clean the sheet

1. One address per cell in a single email column, no spaces or trailing punctuation.
2. Remove duplicates with Data > Data cleanup > Remove duplicates in Sheets, or the duplicate email remover.
3. Normalise Gmail addresses if you suspect dots and plus-sign duplicates, using the Gmail address normalizer.
4. Remove anyone who asked not to be contacted.

Step 2: Verify the addresses

Two ways to do it:

CSV round-trip (quickest for a one-off). File > Download > CSV, upload on the verify page, download the results with your columns kept, and import the status back into the sheet as a new column.

Apps Script and API (for regular use). If you mail merge often, a small script can call a verification API for new rows. How to verify emails in Google Sheets shows tested formulas and scripts.

Step 3: Filter the merge to valid addresses

Status	Include in the merge?
Valid	Yes
Catch-all	Not in the first send; consider a small later batch
Risky (role, disposable)	Usually no
Unknown	Re-check first
Invalid	No; delete or mark

Most mail merge tools let you send to a filtered view or skip rows based on a column. Use a filter view so the merge only sees valid rows, or copy valid rows into a new tab.

Step 4: Pace the send

• Stay well below the daily limit. Personal Gmail is not built for bulk sending.
• Spread a large sheet over several days instead of one burst.
• Use the tool's scheduling or throttling options if it has them.
• Send a test to yourself first to check personalisation fields.

For cold outreach at any real volume, a dedicated setup with separate sending domains is safer than your main account; see cold email domain setup.

Step 5: Handle bounces quickly

If anything bounces, read the message. Paste it into the bounce message analyzer. Mark bounced addresses in the sheet so the next merge skips them. If many bounce, stop and re-check the rest before continuing.

Mail merge from Outlook

The same principle applies to mail merges from Outlook or Microsoft 365: they send from your own mailbox. Verify the list first, and keep volume well under Microsoft's limits. See fixing a restricted Microsoft 365 sender if a mailbox gets blocked.

Checklist

• Single clean email column, duplicates removed
• Addresses verified; status column added
• Merge filtered to valid only
• Volume well under your daily limit
• Test email checked
• Bounces marked after sending

When a mail merge is the wrong tool

Mail merges from Gmail are great for small, personal sends: event follow-ups, customer updates to a short list, or a handful of introductions. They are the wrong tool when:

• The list is in the thousands and needs sending every week.
• You need proper unsubscribe handling across many sends.
• Several people need to send to the same list without stepping on each other.
• The recipients have never heard of you.

For marketing to opted-in subscribers, use an email service provider with list management and one-click unsubscribe. For cold outreach at volume, use a sequencer with dedicated sending domains and inboxes. The complete cold email guide covers that setup in order.

Keep a record of who you emailed

Mail merge tools usually add a status column to the sheet. Keep it. It lets you avoid emailing the same person twice, track who replied, and remove bounced addresses before the next send. If you merge from several sheets, combine them into one master list and dedupe new sheets against it with compare two email lists.

Verify your sheet

Download the sheet as CSV and upload it on the verify page. You get 100 free email checks when you sign in with Google, no card, which covers a small merge or a sample of a large one.