To send multiple attachments to a recipient of your mail merge, all you need to do is add the Google Drive URLs of the attachments in the respective cell in the Attachment column and separate URL with a comma.
- Open the Google spreadsheet for the mail merge.
- Add multiple URLs in the recipient cells and separate each with a comma.
- In Google Sheets, select Add-ons > Yet Another Mail Merge > Start Mail Merge.
- Click + Alias, filters, personalized attachments.
- Select Attach files in column “...” to emails sent, and click Back.
- Click Send emails.
Your recipients receive an email with multiple attachments.