Define Gmail settings if you want to send your mail merge from a different email address.
1. Add the alias in your Gmail settings
Click the gear icon on the top right corner and follow the link to See all settings.
Select the Accounts tab. Next to Send mail as, click Add another email address to use an alias when sending your mail merge.
A window opens. Write a name and the email address you want to use as an alias.
Make sure Treat as an alias is checked.
Click Next Step.
Click Send verification.
From the Gmail account, you want to add (in our example: email@example.com), open the email Google sent you and copy the code. Go back to your primary account (in our example: firstname.lastname@example.org), and paste the code in the verification field. Click Verify.
The new email address appears next to Send mail as in your Gmail settings.
If you need more help configuring additional accounts, read this article in Google Help: Send emails from a different address or alias.
2. Send a mail merge with your alias
Open your spreadsheet. From the Extensions menu, select Yet Another Mail Merge: Mail merge for Gmail > Start Mail Merge.
Select the draft you prepared for your mail merge and then click '+ Alias, filters, personalized attachments'.
In our example, we unchecked the tracking option.
Select your alias email address and click Back.
Recipients receive an email from the alias account.
Please note that the alias feature does not work with the test email option. Learn more: The 'Send from' field (alias picker) isn’t working