The complete guide to Google Sheets mail merge in Gmail

Mail merge is the practice of sending a batch of emails where each one is customized with data specific to that recipient — their name, company, role, or any other field you track. Done right, it's one of the highest-ROI outreach strategies available. Done wrong, it produces the kind of emails everyone recognizes and ignores.

This guide walks through the entire CMass workflow: from preparing your Google Sheet to reviewing a live preview of your personalized emails before hitting send.

Step 1: Prepare your Google Sheet

Your Sheet is the source of truth for the campaign. CMass reads every column header as a potential merge tag, so column names matter.

• Use clear, consistent column headers: First Name, Last Name, Company, Email, Role. Avoid spaces or special characters in headers.
• Put the email address in a column labeled 'Email' (CMass auto-detects common variants like 'Email Address' or 'Work Email').
• Add any context field you want available to merge or AI personalization: LinkedIn URL, Industry, Last Contacted, Custom Note.
• Make sure every row has a valid email address — blank or malformed emails are flagged and skipped during the import review.

Step 2: Open CMass in Gmail

Once CMass is installed from the Chrome Web Store, a CMass icon appears in your Gmail sidebar. Click it to open the campaign panel. The panel is split into four tabs: Recipients, Template, Follow-ups, and Settings.

Step 3: Import your Sheet

In the Recipients tab, click 'Import from Google Sheets'. A picker shows your Drive files — select your sheet and choose the tab (worksheet) if you have multiple. CMass reads the headers and shows a preview table with the first 5 rows.

• Duplicate emails are flagged — CMass will ask you to deduplicate or proceed.
• Previously unsubscribed contacts are automatically excluded.
• Invalid email formats are highlighted so you can fix them in the source Sheet before re-importing.

Step 4: Write your template with merge tags

Switch to the Template tab. Write your subject line and email body. Use double curly braces to insert merge tags — they autocomplete as you type based on your Sheet's column headers.

• {{First Name}} pulls the First Name column value for each recipient.
• {{Company}} pulls the Company column.
• Any column in your Sheet is available as a merge tag.

If you're on the Pro plan, toggle 'AI personalization' on. Claude will generate a unique opening line for each contact using all available columns as context. You can see exactly what Claude will write for each recipient in the preview panel before sending.

Step 5: Set up follow-ups (optional)

In the Follow-ups tab, add up to 3 automated follow-up stages. For each stage, set:

• Delay: how many days after the previous email to wait.
• Condition: send only if no reply, or always send regardless.
• Subject and body: can re-use the same merge tags and AI personalization.

When a recipient replies to any email in the sequence, CMass detects it and stops further follow-ups to that contact automatically.

Step 6: Preview and send

Before sending, use the preview panel to browse how each recipient's email will look — merge tags filled in, AI personalization applied. This is your last chance to catch issues.

When you're ready, click 'Start Campaign'. CMass queues the emails through Gmail's API, respecting Gmail's daily sending limits. The analytics tab shows opens, clicks, replies, and bounces in real time as they come in.

Tips for better results

• Warm up new Gmail accounts gradually — start with 50/day and increase over 2 weeks.
• Keep bounce rate below 2% by verifying emails before importing (tools like NeverBounce or ZeroBounce work well).
• Subject lines under 50 characters get higher open rates on mobile.
• Send Tuesday–Thursday, 8–10am recipient's local time for highest open rates.
• The best follow-up adds new value — don't just say 'bumping this up'.